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Awesome! Thank you so much for your help. You rock!

Ah - okay, I'll see if I can do that. I'm not sure if I can though because of the way the ecommerce platform is setup. Yes, the sitemap has been corrected and has all non-https URLs in there. I mean, will google eventually "catch up" or is this a big issue that I should try everything in my power to fix? (It's not all links coming in via organic - just a handful but it's important as those are great leads). Thanks for your help!

Hey There I've not used Squarespace but this looks like your answer here: http://help.squarespace.com/guides/how-do-i-create-url-shortcuts-or-mappings I think they are calling them "shortcuts" or "mappings" and not "redirects" but looks like it achieves what you need. As others have said the global catch all isn't very ideal, you should definitely individually redirect old pages. Hope that helps!

Oh well, as you mentioned "rebrand" I guessed you were able to also merge the two, by using one site to cover all, like most manufacturers do (apple, samsung, sony, etc). Anyway, in this case, I would suggest you build different content for both sites. In the manufacturer site, you can have technical specifications, let's say it builds computers, then in the manufacturer page you list technical aspects of the chips, motherboards, manufacturing process, etc. While in the sales front you "SELL" the end product, show how it works, you can probably add videos of the product in action, etc. By following that process you will end up with "similar" pages, but sites that actually read totally different; and you won't need to nofollow or noindex anything...

Yes, if you cover your bases with testing, and 301 redirect everything, you should be in good shape.  That said, it's important that the new site loads quickly and has a great user experience.  If it's slower than the new site, that won't be helpful for user engagement. We recently migrated a client from OS Commerce to Magneto, and they saw their conversion to purchase rate increase in the hours after we switched over the site.  I think that the new design helped, and it made it less confusing to the end user. Let us know how it works for you... -- Jeff