Please note that these are all just my thoughts and opinions on my experience with the game. I do not mean any ill will with my comments. At no point do I classify myself as a professional with critiquing or reviewing things, so this is fair warning.
So right away (after having to redo the map because Deku got doubled by Mr. "capped Speed Great Knight"), my first immediate thought is Deku. I like the sprite, I like the unique animations, but in a fight, they're probably the weakest of the bunch. Gets doubled by the reinforcement Mage Knights on turn 7, and it seems that extreme crit boost only affects Gleipnir. There were also moments when, even though I had units in range, the Mage Knights didn't even bother attacking anyone and just surrounding my units.
I like how Vanix's Rich Spear is just a Brave Lance that can be used at range. That's pretty fun. He's also just an Ephraim recolor...which is something, I guess. Despite having 0 crit, I like Riese's Dark Camera, even though I only ever use it at range, but now I think I need to talk about the one elephant in the room I didn't like, and that's the two absurdly overpowered enemy units at the end of the first map.
While the General is only annoying because of his weapon and the gate, this guy is another story. If you don't use the special sword you get off the Dracozombie, you must use Sanagi and slowly chip damage him or he
will kill someone, without a doubt. Personally, I'm not a fan of being showhorned into only having two options for a threat, especially when 3 of your 4 units are worthless against it. You have the scrublord enemies that all bite the dust instantly, but then this guy just murders your units like he's going out for a stroll.
The second map, at first looked a bit intimidating since almost none of these units have any Res and there's a Shadowshot Gorgon, but getting another unit with a 1-2 range sword was nice...until the 16 cavs showed up. At least they don't run on FE6 logic like the Paladins and Mage Knights from the first map, but now it just feels inconsistent. Another problem was the Generals having tons of health. Why do they have tons of health, but the Mage Knights, another promoted class, were about as average as they should be while these Generals are running around with Silver Blades with 80+ HP. But on another note...
Did we really need a boatload of Bishops when weapon durability will likely already be running low from the first swarm of enemies, plus the entire first map? Like, since I was already near the boss, it wasn't a problem, but I did start using the speedup button due to the sheer number of enemy units I had to wait for.
Speaking of which, those 16 cavs drained my Rich Spear and then Vanix was stuck with no weapon at the end of the second map. Why does he have a Gold Orb if you can't sell it to get another lance on the off chance you run out on your current one, or better yet, have him run two lances like how Sanagi starts with a Killing Edge and Wind Sword. Once he ran out, I kinda ended up just charging the boss and missed an 80% hit because my luck sucks, but Deku got the killing blow with a 56% Gleipnir hit...because of course I can miss an 80 but land a 56 just like how everyone but me gets the "30%" Scald burn chance in Pokemon.
But back to positives. Rosia literally looks like a pink haired Eirika, but I liked her animations in battle and her personal sword was very fair and balanced (and not in the sarcastic way I say blatantly broken things are fair and balanced and I liked Lizy's combat sprite. I will make zero comments on the writing because of the warning beforehand that this was for fun. If this was a serious project, I'd have some words about the writing.
So overall, while I had fun, the general balancing, I feel, needs some work. Maybe buff up Deku a little so they're a little less squishy and a little faster even with Gelipnir's weight (I handed the sword to Sanagi right away because she got better use out of it), possibly give Vanix another lance so you can either preserve your Rich Spear for when you may actually need it or access to a shop so you can sell off that Gold Orb and buy some lances or tomes, since you get no light tome user against these Shamans and monster units. The 3 Elixirs are fine as if and makes you have to carefully consider when you need to use them. The swarms of enemies, maybe cut down on a bit. The Bishops at the end of the second map are just unnecessary padding that'll eat up time, and maybe 16 cavs is a little too much. Cut that in half, and remove the "FE6 we can move after we spawn" BS on the Paladins and Mage Knights on the first map (the Soliders are too far away for it to matter).
As for those Generals, do they really need 80+ HP when you only have 2 magic users, one with limited weapon uses (the Wind Sword sucks at range in my opinion, so it hardly counts), and the Monks that spawn the turn after the Generals are pretty worthless since you're going to get swamped by Bishops 2 turns later, anyway.
Anyway, those are my thoughts. If you do decide to go and make more, I wish you the best of luck with it.