Domain Access, Subdomain, or Sections?

Need a little advice on the best direction to go please.

I'm creating a site that will have a landing page, example.com (more like a two door portal), giving access to two branches, branch1.example.com, and branch2.example.com.

Criteria:

• branch1.example.com, and branch2.example.com will each have unique "Home", "About", "F.A.Q." ect., where the relative URL of each are the same, e.g. branch1.example.com/home, and branch2.example.com/home
• branch1.example.com, and branch2.example.com will each have an Ubercart store with branch specific products in the respective stores.
• In addition to a link to each branch on the two-door portal at example.com, each unique branch will also have a link to the opposite branch site, as well as back to the portal.
• Visitors to the either branch1.example.com, or branch2.example.com should be able to add items to the shopping cart, then, if so desired, jump over to the opposite branch to make additional shopping selections, then ultimately "checkout", where both branches would share a single checkout.
• A link to the common checkout, would be available on both branches as well as the primary landing page.
• Other than a shared checkout, neither branch would be likely to share any content.
• Administrative login should also be in one location, where privileges would determine whether that administrator has access to all, or only a specific branch.

I've looked at Domain Access, Subdomain, and Sections. All three appear to, at some level be viable options. Domain Access looks to be the best choice; but, it also looks a bit overwhelming to me, on the surface.

Do you think that Domain Access is the way to go based on the above criteria, or do you think it is overkill for this project? I sure could use some insight on this. I welcome any feedback. Thank you!