[badmanbren]

No not everyone is expected to be in a gang but most active players tend to be in one.
Yes for upgrading a gang it costs more, I think it costs 25k to make a gang, 20k to up capacity to 4 and 25k to 5 that's more than likelly why you see many lower gangs at capacity 4-5. For the record, with the bit stating you see not many gangs with 10+ members, Pestilence has the current largest capacity being at 19... appreciations to the massive help from the LONEGunman. (Pullo)
Yes and you will get bugged if you're active and not in a gang, few more levels with you not being in a gang it may be my turn, hehe.