Your crew can consist of up to 10 people at the same time.
You will be able to order your crew around in-game.
You can release someone from your crew at anytime. Then you wont have to pay them. They will stay among your contacts, so you can call on them at any time to get back into your crew. Reasons for doing this, is that during different phases of the game, you will need gangsters with different skills. Then it might be reasonable to release some gangster from your crew in order to recruit some new ones for a specific job or just for an certain amount of time.