Since it's a flat bonus, I think I should be using them to boost someone with a low base stat like Toad Lily's attack. I'm curious to hear what you all are doing though. Or do you just give them to your favorite girl or are you saving them?

You use it on your fav waifu, that's about it. The one girl you like a lot and want to keep in your squad forever.

Using all ampys i get on my Orchid.

Same here, gave 'em all to Orchid =)

I'm giving them to Convallaria. Going to keep her as my 1st squad leader for a long time.

I'm waiting for edelweiss.

The one 6* I have, since I figure no matter what comes in the future she'll find a spot somewhere on my team.

Is there any need to hoard like 10 of them before using them? Or can we use them as we get them?

There are no stat reason for hoarding them till you have ten, just if the singles you give to your girl do NOT raise her level, by all means. If its going to raise her level then you have to be aware the next level is going to be more expensive for all other combinations. And obviously none of this matters if she's already at max level.

The only reason to hoard ampies to 10 (and beyond) is if you want to feed them to a girl you do not have yet. Then the can be used as exp and ampies (and also cost effectively) when the your new girl is still low level.

Strawberry. Always Strawberry.

Event Girls First, since they will be the strongest for a long time, with 5 Skill and 4 Slots. After that you can pump them in your favorite girl which you want to use like forever.