Hey there! I'm also a new player so I'll weigh in my experience after my first few games! Admittedly the keeping track of math thing is a bit difficult, and yes, it can be pretty overwhelming. The exact mechanics for spells are something that have been confusing and given me a few flubs here and there.
However, with a little bit of practice you can pretty much "guesstimate" your incoming damage as an NPC. Most of the time as a PC you won't be getting hit so frequently that you can't easily keep track of the numbers. If you start to get overwhelmed with numbers, it's generally easiest to assume that you're down, especially as an NPC. The whole "doing math while being beaten with foam" aspect of the game is one of the areas that has to be taken with a grain of salt because unless you're some kind of savant you're gonna have to just do your best and err on the side of being a good sport.
Another thing is that (almost) everyone in this game is a really really good sport. They know its a game and if you start to get overwhelmed they'll help you out! You should DEFINITELY NPC a few games before you get going with your PC. I got a little over-excited and PC'ed after only one NPC game and now that I'm bit deeper in the game I really wish I had given myself a better idea of my play style before I made my main character.
In the end though, I know you can do it! It SOUNDS like too much at first (when I first read it I was like, NO WAY) but it's really manageable.
Hope that helped!