It's normal for anime, manga and their Western counterparts to have one arc at any given time. Will it be confusing if there are multiple arcs at the same time, all of them involving the MC? I mean, it sometimes happens during real life, right?
Yes, it's very common in all forms of mainstream story-telling.
It's called the "A plot" and the "B plot." There is a reason why they are named like that. The idea is that you should make the "A plot" your main focus and dedicate the most time to it, while slowly progressing the "B plot" as an under-current to the "A plot." Normally, "B plots" are stories that would be a lot shorter if they were told all at once, and only go on so long because they are stretched out and told in increments over the course of the "A plot."
In long-run stories though, it is possible for a "B plot" to be extremely long and stretch out over the course of multiple "A plot" arcs over the course of a larger story. In these scenarios, it is often the case that the extended "B plot" is actually more of a through-line that ties all of the smaller "A plots" together. An example would be in One Piece, the quest for the treasure at the end of the grand-line in order to become pirate king. Or, in Detective Conan, the quest to ferret out details on the black organization.
A few final details. While it is normally the practice to have only one "A plot" arc active at a time, you can have as many "B plots" as makes sense for your story. There is also such a thing as a "C plot." A "C plot" is usually a sub-plot that is generated from one of the "B plot" arcs. They tend to be comparatively short, and serve a purpose of supporting the "B plot" somehow. You never hear about a "D plot." This is because if your "C plot" actually spawns a "D plot," then you are way too deep in the weeds and you have probably already lost your readers by that point. So, I recommend against "D plots." Reviewers actually deride writers who create them as having written an absolutely confusing mess of a plot, and use the fact that "D plots" exist to be an example of why it's so bad.