I apologize if this question has been asked far too many times throughout various FE:TH topics, and I'm not sure how to word my feelings exactly, but here's my thing:
I have been trying to get into Fire Emblem for what feels like forever now (used to love it casually on GBA), but I always get turned off because I lose a bunch of battle attempts in a row and feel like I don't know how to succeed or feel like I never get a grip on the mechanics.
With this one, my concern is that I would make a decision on a skill for a character that may be 'wrong' or 'not optimal' or that I would build a character the wrong way and put myself into a hole where I will continually lose and mess something up for the long game.
Are any of these concerns really valid? I feel like I'm just being irrational honestly and maybe I should dive in. I LOVE everything else about this title and it technically would be my first one I would try to deep dive into (considering I've never played more than a few hours other than on GBA).
As someone new to the series (and who has not played tactics games much in general in a long while), I think you will be fine! For starters... it's been very easy on Normal, haha. Most difficulty has come from me carelessly using units who were not actually fit for the fight, and even then it has not been too bad, I just felt like bringing them was wasteful when I had to barely use them. And they give you the ability to rewind your actions (with an increasing number of uses per fight) so you'll be able to undo mistakes. I think the mechanics could still stand to be explained a lot more, but they do clearly indicate stuff like who enemies are going to target, the chances of hitting + the damage they'll do, etc. which makes it very easy to make strategic decisions. Plus, you can do Casual for no perma-death; I still rewind to avoid losing people, but it means if I get very frustrated I can always stop caring and win the battle without worrying.
The training stuff can feel a
little daunting but it does a good job of showing you what characters are strong at. Like it literally shows you what they'll level faster because they're good at it, sometimes along with one skill they're currently bad at and then will become good at + gain an extra ability once you train them in it a bit. From there, it's a little less intuitive/the menus can be a hassle at times, but you can look at all the classes they can become later on and pick skill goals to aim for based on what they'll be good at and the classes require. Some of that has become a bit frustrating now that I'm later on, cause I'm realizing that certain characters kinda need to level in some skills that I didn't realize were still so low; even then I don't feel like I've done anything "wrong", though, just needed to write down a note or something instead of wasting time fiddling with the menus each time.
And on top of that, classes are gained via tests they have an increasingly high % chance of passing as their skill levels approach the requirement. So even if you really messed up, as long as they have >30% chance of passing you could always just brute force it by trying each week (and reloading on failure- just to save the cost of trying, cause the roll used to decide the test is already set in advance).
So... yeah. I think it's easy to avoid that kind of situation without having to super overthink and research in advance! You should be fine.