Honestly, that sounds like a great idea! Though, I would think a temporary upgrade sounds more like a spell scroll or other magic. Actual training sounds more like a permanent upgrade.
Though you could slap a gold fee on the training so it costs gold to train a specific stat, and if you want to scale it with progression, make a full stat point cost the current girl's current stat level, tripled in gold. This way, it gets more expensive to train, the higher level the girl is, so you gotta choose where to spend your money more and on who.
So maybe temporary magic stat boosts from the Magic Academy and permanent stat upgrades from training... Anywhere potentially. Maybe have the Carpenter Orc Build a Dojo near the Brothel where the girls can train, after unlocking Suki, so they can train and do sexual sparring together.
I also noted the unique character animations are gone, and replaced with the more basic recolored animations. I really liked the unique ones, even if they're just works in progress! <3 (Edit: I caught up on the Dev logs, ignore this. <3)
Just a few suggestions! I love this game and I like the direction you're taking it in!