Hi,
Regarding giving gifts, it's only on your side, it all comes down to get being suspicious of you, of you end the night and:
- leave her naked
- don't clean cum
- let glasses guy see her naked
She becomes suspicious - she won't accept any item besides normal gift. Either way few nights (5 or 6) or until loop reset.
As for other girls, yes dev has plans to include some sexy scenes with other girls, not sure they will be available at night like Yuna.
Hope this helps,
Cheers