SSL, Multisite, domain mapping, and Marketpress Global...what do I need to know?

I have a 4 stores under one multisite install with sub-directories and mapped domains. I want theme all to share a shopping cart and I understand that Global cart Marketpress only allows Paypal express.

Regarding security, does Paypal express negate the need for a SSL for the checkout process?

Should I still get SSL for securing customer detail pages?

Will I need a Wildcard SSL to handle all of the domains, or will one ssl for the root domain work?

Any and all suggestions are appreciated.