Yes, if you were addressing more than one person you would say for instance 'Abbracciatemi', meaning '(You, plural) hug me'

No, verbs do not change to match the gender of the person(s) performing the actions. Adjectives (attributes like young, old, nice, foreign, etc) do. I see you are already aware of the rule that if you are describing a group of 99 women you use the feminine adjective, whereas if the group contains 99 women and one man you must use the masculine one).

I thought the imperative was the polite 'you' form of the verb - or is that what you've done here.

Would it change if you were addressing more than one person?

Also, in the group case. would this be one of the cases where it changes depending on the number of women in the group?