Choosing the right module.

Hello
I'm planing to turn my actual site into a multi site. After comparing the different approaches I decided to give "Sites" a try first.
I just want to make sure that I'm going into the right direction:

The project is multilingual.
It has a quite complex structure of interconnected content based on node references and taxonomy.

* In the beginning there will be 2 sites, later I might add up to 10. Each has a different domain or subdomain.
* Performance is an important issue, as the site seems to be to slow already.
* Each site needs an absolute independent theme and its own front page.
* They will share the same content. I will filter the presented content on a theme level (templates, bocks, views).
* There is no need for site related access restrictions (Even if I might use that option for one single content type, in case it is easily available).
* It would be good, but not nessesary, to create a connection between the users and the site they registered on (perhaps with "auto assign role").
* It would be perfect to be able to override variables on certain sites. (As a way to change the Amazon access code for each country, what is not offered by the Amazon module: http://drupal.org/node/396554) Is this posible with the "sites" module?

To me
'Domain Access' seems to be too heavy and too complex about the node access structure.
'Virtual Sites' seems to be abandoned and not flexible enough.
I still don't really understand the approach of 'Spaces'.
But 'Sites' seems to offer most of what I need.

Am I right?

My main doubt is about SEO. Is there a way to avoid beeing identified as canonical content?

Thanks for your attention.
Achim