Late but something you should be aware of is that FE3 has a notoriously annoying dismount system. Game doesn't really ease you into it and its implementation via game design outside of a section of chapter 1 of Book 2.
Dismounting is a gimmick added to FE3 where you can have mounted units (Cavalier, Pegasus knights, etc) dismount and walk around on foot. While dismounted the unit are all changed to the "knight" class which can only equip swords besides the "Horseman" class which instead is changed into a Hunter (Hunter is a separate class that's units can be promoted/upgraded into a Horseman). When dismounted have a reduced mov stat but (in the case of cavalry) can better travel over mountains and forests.
The main idea behind it is immersion with no horses being ridden around indoors, nerfing the very powerful cavalry classes, and giving horse units the ability to cross mountains and forests. Sounds cool but there are problems, namely...
Units are now locked to swords, which really suck unless you have high strength and agility or that sword is a Levin Sword (sword that attacks with magic damage). Doesn't help that some of these units already don't have a fantastic damage output when they join. You're probably gonna end up using Cain, Abel, Hardin, Jagen and maybe a promoted Castor though in terms of hoses assuming none of them die
Makes it so only armored knights and generals can wield lances indoors, which is an annoyance since a lance is the best weapon in the game and said lance is iconic in the series
It requires you waste a turn when dismounting and (iirc) mounting as doing so ends that specific units turn.
Basically just, be aware dismounting is a thing. It's not AS dumb as it is in other games but it can be annoying.