Subsite for Membership

It's only just occurred to me that I should probably build the membership / store section of my website on a subsite, to keep the main site - fast and lean for marketing.

As much as I love Upfront, am i right in thinking that I should use a 'legacy' theme if I want to integrate properly with these plugins?

Membership
MarketPress
Affiliates
BBForum
Crowdfunding

( Sorry if I've got the names wrong - but all WPMU apart from BBForum )

And wait until upfront is compatible with all those plugins?

Thanks