Where should BuddyPress be installed in store network?

I’m new to MarketPress and am setting up a test site for a store network. Like everyone, I’d like to avoid making wrong choices in the initial setup. The main site will have a product-oriented home page, and there will be a BuddyPress community for the whole network (not individual sites). The client wants a main store with her own products plus products from members’ networked stores. A Global Cart will be used to avoid shopping cart chaos.

I have several questions about the setup:

1. What works, or works best, with a Global Cart, subsites in subdirectories or subdomains?

I can use either one, but have always gone with subdirs in other Multisite installs because it provides more separation and clarity. (No add-on domains will be used.)

2. Where should BuddyPress be installed when it’s not the focus of the home page?

In a subfolder of the main site? In a separate subdomain?

I found the page with wp-config.php options that tell WP which blog is home for BP. Does storing member profiles in the root work if BP is in a subdomain?

3. Does the store work alright when products are added to the main site as well as subsites? Or should the site owner’s store also be in a subdomain/subdirectory?

Thank you for your insights. Sorry to ask so many questions. Short answers that point to the right path would be most welcome.