On here, by being the first author with a large following to come here and tell all my other readers to come check the platform out just a couple of days after launch, so I got rewarded with a 24-hour sticky on the top spot of SH's updates things on NU for bringing over some decent traffic. Then I may or may not have dominated like half of SH's old trending system for months. I always felt bad about that.
But on RR, where I started off that had and still has far more competition - just writing what people want to read. My titles at the time weren't exactly that clickbait-y and I used to have extremely shitty covers before I started commissioning them since I have a very strong rule against using stolen images. I only ever used copyright-free pictures and shittily edited them in Photoshop. They were the opposite of attractive covers and I have a few readers now who told me they avoided reading my stories until I had real covers for them, but they came after most people did. That aside, I just wrote what I wanted to write and what I would be passionate about. What I wanted to write was what people wanted to read, and my quality was good enough for them, so I got exposure from persistence. I never asked for review swaps or anything. Never advertised. Never recommended them. Never even talked about them to others. I just let my stories stand on their own. If people liked them, they liked them. If people didn't like them, they didn't like them. The only luck involved is that what I genuinely want to write is what people want to read. I get to pander to people by pandering to myself.
So, to answer the questions specifically:
1. It felt great at first. The appeal kind of wore off, though. Comments are comments. Back in the day, I'd fangirl over just getting a single comment. Now, it honestly doesn't really have any effect if a chapter gets 0 comments or if it gets 50+ (in RR's case).
2. I got successful by writing well and writing what people want to read. I'm "lucky" but strictly only in the sense that what I want to write is what people want to read, so I don't have to write what I'm not truly passionate about. However, you don't need this luck to be successful if you don't mind selling your soul a bit. There are plenty of successful authors, especially in the erotica community on Amazon, who treat it as easy money but don't actually care for it. It just beats a "normal" job for them. As long as there's an audience for what you write and you have at least decent quality, you can bring in the followers.
3. I didn't promote at all at the beginning. I've always kind of figured that, you know, the people who get successful are almost never the ones you see trying to push their story everywhere. If you have to try and advertise your story everywhere to get followers, that's not a good sign. Nowadays, though, I advertise to people who are already my readers. When I post a new story, I'll advertise it on my current stories, Discord, and my Twitter, but to nowhere else.
In the end, the most important thing is that people want to read what you're writing, and this is affected by your quality of writing and what genres you're writing. If you're writing in a popular genre and you have high-quality writing, good job. You're going to do fine. If you try that and you're not doing fine, then you're probably not properly hitting the beloved themes/tropes of that genre or your quality isn't as good as you think it is. In the vast majority of cases, it's the latter.