Something I think could help out alot and remove confusion is upon creating a gang aswell as selecting a name for your gang you also select a tag, when a player joins that gang the tag auto applies to them infront of the name, This could also allow gang leaders/founders to pick a colour for there tag so [SP] Excel to [SP] Excel just for a little bit more fun.
Regarding this, Server staff could develop certain gang base designs maybe like 3-5 options for gangs to choose from. Some designs may be big bases with many features that would cost more $$$ however there could also be smaller options that cost less $$$, It all comes down to what the gang is interested in. Gang owners can then upgrade/downgrade or even change design of there base for a cost.
I feel as If there could be issues with a communal storage so with the ranks in the gang as you mentioned you could do It so the storage is private and everyone is allocated a certain ammount. A gang leader would have more storage space than a member of the gang maybe like that?
However when being raided by cops all items would show in the inventory.