I am currently working with a team on a website and we have some important questions to address:

We have a storefront section and a resource section to our website. We are contemplating putting the storefront of general merchandise (ie. shirts, office supplies, plush toys, posters) on it's own website, and the resource section for teachers (ie. book store, forums, blogs) on another website with two completely different domains. Both could have shopping carts, but both could use different branding for different demographics (ie. teachers vs. general public). Would it be better for SEO to have both of them unified into the same URL and only use one shopping basket? Have the storefront as a subdomain of the website and use the same URL? Or would make no difference in terms of SEO to create two websites (at seperate domains) and build them as seperate sites with seperate branding, and then link to and from between each website? The question we are faced with is: would it make more sense in terms of Google's standpoint to have one store front website and one resource website, or to merge them both into one unified site?

Also, the website we are planning this for has about 8 years on the existing domain. It has been around for quite a while on that domain and we wouldn't want to lose any SEO on it. However, we have picked out a new domain that we like a lot better and we would rather use that domain if possible. Is it possible for us to transition our website over to the new and improved domain and also transfer all of the SEO to the new domain with it? We just don't want to be penalized from Google for doing it.

And if this domain aquisition is indeed possible, how exactly is it done?

So my two questions are:
1) does it make any difference to the SEO to have 2 seperate websites (store / resources) vs. 1 unified website (store + resources) and how do subdomains play into this?
2) is it possible to switch domains and not be penalized for it or lose any SEO?

Thanks for your help!