Sure. I'll counter cause I got nothing better to do and it seems fun. Spoiler again to minimize space.Then allow me to respectfully disagree.
Look, are you writing a story about Sword and Sorcery with a dash of Isekai, or are you writing a LITERAL ROLE PLAYING GAME story?
I am, technically, writing a LitRPG, by most standards. All three books are in the same setting and have, what people "call" LitRPG elements. Do I consider it LitRPG? Well, parts of it will be, but not yet.
If you are writing a LitRPG, you are the DM. YOU. THE AUTHOR. You are DMing a Game. In this game, the "Player" (your MC) knows they are in a game. So tell me, HOW DOES THIS DIFFER FROM ANY OTHER ISEKAI?
The difference is, the Player knows the GAME SYSTEM.
If the game system itself is not a major focus of your story, and how the MC interacts with THE SYSTEM, then why write a LitRPG? Just stick with a normal S&S/Isekai. Your reader, if they are coming to read your story, is being told, "THERE WILL BE A GAME SYSTEM AND THE MC IS GONNA FUCK WITH IT". No. Seriously. You put LitRPG in your tags, that's what I expect. That's what MOST READERS will expect.
Now, how do you fuck with the system?
Well, in D&D d20 3.0/3.5, there is an item from the AE&G book called "stilts". Yes. Stilts. As in, you put them on your feet and you are taller.
THEY. ARE. BROKEN.
Why? Because the way the stilts are written, they make your speed 20. Normally your speed is 30, so these reduce your speed by 10, right?
NO.
YOUR SPEED BECOMES 20.
Your speed is 5? Put on stilts, you are at 20. Some versions of attack spells make your speed 0. However, you can apply buffs and debuffs in any order you want. So you are speed 0, but you apply the stilts last, now you are speed 20. Briar Patch? Who cares? Evard's Spiky Tenticals of Forces Intrustion? HAH!
You wanna put on a suit of Thaauld Stone Plate (maybe the best non-magical armor in the game) and carry 10,000 pounds of equipment?
Strap on a pair of 2' tall stilts, pass a balance check of 8, and stroll along at 20 feet a round AND have a +1 to hit from the High Ground Advantage. All from a pair of 6 copper stilts.
Profession: Basket Weaving Sounds useless, right? But you can make items out of wicker with this skill. You can make... Wicker Armor.
Okay... so it's JUST AC: 1 armor. Who cares-
Now I'm adding on thorns so it's a weapon.
Okay... well it still is.
I'm using the armor improvement rules and using my massive Basket Weaving skill to improve the damage and armor on my Wicker armor. Also, it's masterwork, Wicker Armor so it also is lighter and has no movement penalties.
Okay. Well then I suppose...
I'm using my cantrips to distill salt from the ocean. Salt is very expensive, so I'm using it as a material component to enchant magic items. Now with craft arms and armor and craft wondrous items... Well, basically everyone is going to have a +38 to hide and move silently.
While wearing a suit of armor made out of wicker?
Yup.
STOP! JUST STOP ALREADY! WHAT IS THIS MONSTROSTY???
That was an actual conversation I had with a player. I ran an adventure where the players were stripped naked and thrown on a prison island. The player, systematically outfitted the entire party with FUCKING WEEDS AND SALT and instead of sneaking off the island, took 2 weeks to prepare in hiding and then OVERRAN THE PLACE.
That is what a LitRPG is supposed to be about.
When someone knows the rules so well they can take the foundation of the cosmos and fuck it up so bad the very underpinning laws of reality itself wind up sitting in a shower cleaning itself with a brillo pad while weeping and rocking back and forth as it whimpers, "I will never be clean again. I will never be clean again. I will never be clean again...I"
And the player DID it with a 6th level wizard.
In order to pull this off, YOU NEED TO KNOW YOUR SHIT. You need to know the rules. The reader doesn't, but YOU DO. If you break your own rules, the veil is lifted. The reader will figure it out that YOU ARE MAKING SHIT UP AS YOU GO ALONG, and in that moment, the illusion is broken. No longer is this some MC who is the smartest guy in the room using fucking WEEDS AND SALT to build an unstoppable army, but an MC who is PROTECTED BY PLOT ARMOR.
Nobody wants to read about the guy protected by plot armor.
We want the MC who is doing the god damn impossible with next to nothing. We want MacGuvyer. And the OLD version, not the new TV show. We want an MC who can be stripped naked and dropped in the middle of hell and then somehow, figures out how to win. Because WE love that guy. We root for that guy. We want to BE that guy.
If all you are going to do is stack on more points and have a running total of how many XP he has earned and how many levels he's gone up... well... the rest of your story is going to have to be awesome, because that part is going to be doing all the heavy lifting.
A LitRPG has one element that other stories don't. THE SYSTEM. Your system must be well developed, understood, and more importantly, the MC is the one who knows it better than anyone else. The Reader doesn't need to know the rules. You never have to explain them, but YOU MUST KNOW THEM. You must apply them THE SAME WAY. Every. Single. Time. You cannot just make things up as you go along.
SO...
TO the O.P., I suggest you just make things up as you go along.
"What???" I hear you cry.
Look, if you haven't been a DM/GM/ST or any other table top ref in a RPG, then as you write this story, you are gonna fuck up. Sorry, but being a DM is an art form. being a GOOD DM is even rarer. I did it for 3 decades. I know my shit. I can run a game on the fly, making up shit as I go along, because I'm good. Chances are, you aren't.
So, the only way you are gonna learn is to DO IT. Just write the damn story. Don't worry about all this crap because you are going to fuck it up. And You NEED TO FUCK UP, if you are going to LEARN how to do it right.
So, actually, this piece of advice is the best:
If you are just starting out, keep all this advice in mind, and WRITE THE DAMN STORY.
When you screw up, learn from your mistakes, then write another story. Guess what? You will learn and you will do better. That's how this works. Unfortunately, there aren't any short cuts to this process. Write it, and then learn. That's how you'll eventually write a good LitRPG.
And... don't get hung up on labels. Write the story the way YOU want and forget these tropes and guidelines. That's all this is.
A line to guide you in the right direction.
To me litRPG is losing its specificity and has become more of genre. Plenty of sites have plenty of novels tagged litRPG or have it in the name when it's a just a basic system with action and adventure. Not the complex and exploitable system with tons of unique interaction that DnD has. I can't say I like it, but as it is now, I don't think litRPG is limited to in depth systems or a heavy focus on the system. Many don't even have a party of characters and instead just have one who makes friends but doesn't adventure with them which further expands it.
So while I do agree the basics of the system need to be solid, I don't think going super in depth is necessary for it to be litRPG. Stuff like how many skill slots, how high levels and stats should be, if skills can level and evolve, how many classes. what type or if there are classes at all, etc., is super important to figure out, but It feels like the basics.
Beyond semantics, I believe we have a different writing philosophy. When writing, I try to minimize my mistakes when starting something new and by keeping it simple whereas it sounds like you accept making more when new and then trying to learn more from it? For me, I can't write that way. I become too much of a perfectionist when I decide to really work on something. If it becomes too complex I either stall out or I endlessly revise because I don't like how something feels or get bored yet can't force myself to move on. Make no mistake, I don't think it's bad, I just don't think it's for me or necessary to write litRPG as it is now.
So while I do agree the basics of the system need to be solid, I don't think going super in depth is necessary for it to be litRPG. Stuff like how many skill slots, how high levels and stats should be, if skills can level and evolve, how many classes. what type or if there are classes at all, etc., is super important to figure out, but It feels like the basics.
Beyond semantics, I believe we have a different writing philosophy. When writing, I try to minimize my mistakes when starting something new and by keeping it simple whereas it sounds like you accept making more when new and then trying to learn more from it? For me, I can't write that way. I become too much of a perfectionist when I decide to really work on something. If it becomes too complex I either stall out or I endlessly revise because I don't like how something feels or get bored yet can't force myself to move on. Make no mistake, I don't think it's bad, I just don't think it's for me or necessary to write litRPG as it is now.