Advice on MarketPress Setup for Multisite Services Model

Hello.

I'd like to get some help with formulating the technical setup for my web services business model. Any feedback is greatly appreciated.

OVERVIEW
I'm running a multi-site install where the root site is treated as the gateway to all other services operating in the company. Each major service area has its own site built on the network install.

Each service area will be branded separately with its own domain which will be domain mapped under the root site.

I want to setup separate lead generation paths and follow up marketing systems to each of the services independently. I prefer this option than just pooling all services under the one brand/banner so that I can focus my marketing efforts specifically to the needs of that subscriber/client, without them becoming distracted by other offers from other service and product areas.

I can then cross-sell/up and down sell between my separately branded services as required.

PRODUCTS/SERVICES
Websites; SEO, Local Search Marketing, Private Community (BuddyPress), Video Hosting, Web Hosting, PPC, Social Media Marketing, Copywriting, Marketing Systems, Consulting... (you get the picture)

In addition, this may move towards info products and also promoting affiliate products

TECHNICAL
I'm testing out MarketPress and am liking the improvements. Great job everyone!
Also, I'd like to use the MP themes as they are displaying the products in a much nicer way than my current theme does out of the box.

I want to keep my current theme (Thesis) for content areas but a purpose-built MP theme looks likely for product display.

In addition, I'm keen to tap into the Membership plugin, particularly for buddypress membership controls and any others access controls I may add in in the future.

QUESTIONS:
Keeping Separation of Specific Products
Is the best way to segregate each service's products to setup an MP store for each site or a centralised MP site that displays products on the individual site's pages?

Centralised Store vs Separate Stores
Is there a way to serve products from a central store into each site on the network without opening up the view to all products across the network. I'm thinking about wrapping the MP central store into my Thesis pages.
I don't necessarily want to restrict access to other areas, more just hide all the product categories and non-related product lists from view.

Using MP Themes for product pages only.
Ideally I'd like to use an MP theme for just the product pages. I'm thinking about creating a 'store' site using an MP theme from which all products could be served network wide. Can shortcodes be used to achieve this?

Apologies for the length of this. Thanks for reading. I look forward to any replies
Cheers
Paul