is there a decent chunk of story missions to get stuck into ?
also gang's , is there a rating on how friendly you are with them ? like in SA ? and is there any other cool features like this ?
There's over 500 missions all ready to go. Each mission, excluding one off missions like property missions, is capable of being branched if R* chooses. They can release new missions as any time.
Yes there will be rival crews and crews can compete against each other via the Social Club. Not all features of the Social Club are available just yet, so information is scarce.
You can have alliances with crews, but the mechanics of this are unknown as of yet. Not sure what benefits this will provide to the player.
Also, you can hire other crews for certain missions. This feature was implemented to prevent crews from breaking crew hierarchy.