Calwings posted... Join the club. The Chapter 10-11 story hit is definitely a big one for first-time players to deal with.
Just a heads up: that's a terrible idea in this game. There's simply not enough experience to go around to use that many different characters all the way through without becoming severely underleveled, especially because the amount of deployment slots you get in major battles is fairly low compared to past FE games. Even worse, the skirmishes you can use for free grinding scale to Alear's level, so if Alear becomes too high leveled (which they most likely will if you spread your experience too thin like that since you're required to bring Alear in every major battle) then it'll become impossible for units that fall well behind Alear's level to catch up. It's very possible to make the game completely unwinnable and have to start all over because you won't be able to beat the next chapter and you won't be able to grind either.
The closest thing to "using everybody" you can do in this game is to constantly rotate out your weakest older units for newer ones that you recruit later, because the mid/late-game characters in this game are actually really good and sometimes just straight-up outclass the earlier units. Generally, you want to just focus on a core of like 12-14 or so characters most of the way and ignore everyone else. The most characters you can bring in a battle is 12 until the very latest chapters of the game where it goes up to 14, so you don't need more than that.
Unless you're referring to on higher difficulties - I don't feel that AT ALL in this game compared to past FEs. Like I said - I've only ignored maybe 3 of my characters (also I guess the two that came with Ivy, who I JUST got) and haven't had any problems. In past FE games (especially the GBA games) I felt it waaay harder spreading exp too thin.
Either way I'm thinking about restarting and just using only the characters I really like. I also feel like I really missed out for the other reasons I said.