Even if we assume the inverse of all these posts--
Zane Avernathy's (New assumption being: that doc exists and the product is actually complete);
Crazycolorz5's (that the tool perfectly aligns to how you think it should function / you can arrange yourself to the tool as necessary very easily)
MCProductions's (that your project's vision factually exceeds the capabilities of FE8 and that you're good at self-education and dabbling)
I would be inclined to say that people still wouldn't get things done. At least, so my cyncism from having multiple dying husks of projects tells me.
Struggling to get started has, for me and some friends, done nothing but help realize mistakes in our vision. That the very things we believed were necessary were our real stopping blocks.
I said personally for a very long time that I couldn't code but that I could write, but now I realize that I'm the hackiest hack of a writer and I can program.
Generally, though, I find a slogan of my grandfather somewhat appropriate; "make everything as simple as it needs to be and no simpler".
Don't decide you can't do it on the GBA engine until you try. See what limits that engine has, and which ones that you actually hit with your idea.
Then think about how necessary any of that is.
Do you need more than 255 items? ...Probably not.
Do you need more than 127 classes? It's possible, if all classes need two genders and you have a healthy number of cutscene-only classes.
Do you need more than 255 classes? ...Probably not.
Do you need stats to go past 63? ...If you do, why are you making an FE game?
Consider, also, implementations. You can circumvent charge up skills by having multiple skill IDs dedicated to one skill, then have only one of those actually allow you to activate it; then having combat or phase change adjust which of those skill(s) the units have-- that doesn't work for everything but it can certainly work for many.
There are a lot of creative ways to get around what you believe are limits-- and honestly, you can frequently see exceptional creations born out of limitations.