I'd also add that I'm currently prioritizing slice/pierce units on my helper squad if I can, since they're the most useful for helping people farm 12-5, and for the other maps, any strong helper squad works fine (besides weird speed requirements for 3 medals).
Also, ampies seem to be counted for my own power numbers since they just add to the characters stats (like affection), but I'm not sure if they're counted when allies see helper squads. It's really annoying that equipment doesn't show on power though, since it makes it hard to gauge actual strength. My Canola is +1247 ATK, +564 DEF from her equips alone, making her a lot stronger than the power numbers show. Are we sure equipment carries over to helper squads? It would change a lot for me if it didn't.
I'm starting to prefer high HP as the best stat to have, since it's the only one we can't increase with equipment and gives staying power over multiple fights. I noticed my Violetta Tulip dying first very often when I had her in my squad, despite her having around 700-800 more defense than characters like my St. Paulia, because that defense just couldn't make up for having 3k less HP.
EDIT: OK yeah, this looks much better
It already hurt bringing along Bipina with her 215 speed and Paulia with 345, throwing in Lavender just made my squad move like a snail (thankfully somewhat saved by Orchid). Hopefully my allies won't care about slightly less power in exchange for movespeed and another slice unit.