Questions regarding Buddypress/Membership workflow


I just finished reading your Membership plugin manual and I have some questions:

My site has buddypress (and bbpress) installed and I will always want my users to choose a free or paid Membership plan.

Which one should be the registration form to use, the buddypress one or the membership plugin one? Always?

In case it is the Membership one, can the Membership form have the custom buddypress fields? Does it share them with buddypress?

Or it must be a 3 part register? ie: Membership form ---> paypal ---> thank you page ---> buddypress profile update? Please let me know the register workflow.

Once registered, who takes care of the user login; wordpress, buddypress or Membership?

Tank you for your help,