Yoast works well alongside Genesis - as StudioPress were gracious enough to allow a dedicated SEO plugin take over from their built in offering.

You say Wordpress - I say Yoast's Wordpress SEO - which will also generate Sitemaps - alongsite a LOT of other groovy SEO things!

http://yoast.com/wordpress/seo/#xml-sitemap

Rand talks about URL shorteners and their effect on link juice etc here: http://www.seomoz.org/q/is-there-anyway-for-redirected-links-to-still-provide-seo-value - Very good info (as you would expect from the bearded one...)

Okay. After re-reading the question (with my eyes open this time) I understand that the fact that no link jiuce will be passed to Site A (from Site B) is not an issue, rather you don't want to lose the existing link equity when you switch Site B back on and then 301 redirect Site A to Site B?

So, with that in mind - there is no specified 'acceptable' time limit attached to a 302 redirect, so you should be able to redirect without fear of being penalised, regardless of duration.

This is mentioned elsewhere on SEOMoz here: http://www.seomoz.org/qa/view/9994/302-redirect-timeframe

This is an interesting read however: http://www.seroundtable.com/archives/007233.html - just to keep things edgy ;o)

use the rel=canonical on the main page/s to show that they are the original/source/master page of the content.

See this helpful guide:

http://www.seomoz.org/blog/complete-guide-to-rel-canonical-how-to-and-why-not

Don't forget you can also tell Googlebot to ignore certain URL parameters to prevent them being indexed and treated as duplicate content.

"If your site uses URL parameters, some of the parameters may be unnecessary for page navigation. Asking Google to ignore these parameters can reduce duplicate content in Google's index and make the site more crawlable."

This is done through Google.com/Webmasters - Your Domain - Dashboard - Settings - Parameter Handling.

Don't 302 in this case. Infact, don't 302 if at all possible as it passes ZERO link juice - 301 for this and get 90%+ link juice passed on. It does sound counter intuitive - certainly based on the titles MOVED PERMANENTLY etc but it is the best practice in this instance.

301 Moved Permanently

A 301 Redirect is a permanent redirect which passes between 90-99% of link juice (ranking power) to the redirected page. 301 refers to the HTTP status code for this type of redirect. In most instances, the 301 redirect is the best method for implementing redirects on a website.

302 Found (HTTP 1.1) / Moved Temporarily (HTTP 1.0)

A 302 Redirect is a temporary redirect and passes 0% of link juice (ranking power) and in most cases should not be used. The Internet runs on a protocol called HyperText Transfer Protocol (HTTP) which dictates how URLs work. It has two major versions, 1.0 and 1.1. In the first version 302 referred to the status code 'Moved Temporarily'. This was changed in version 1.1 to mean 'Found'.

Extract from

http://www.seomoz.org/learn-seo/redirection

This might help:

"If you have an ASP.NET web application site, and you place a text file named "app_offline.htm" in the root of the site, all requests to that website will redirect to that app_offline.htm file. Basically, if you need to take an entire ASP.NET site offline, you can place some nice message in that file. Then, any new requests to a URL, any URL, in that website will redirect to that file allowing you to do maintenance to the site, upgrades, or whatever. It is not really a redirect though. ASP.NET essentially shuts down the site, unloads it from the server, and stops processing any requests to that site. That is, until you delete the app_offline.htm file - then things will continue as normal and your ASP.NET site will load up and start serving requests again.

A super-cool side effect of this is that any files that are locked by the site, such as a database or other resources, are freed since the application domain has been unloaded from the server. This allows you to remove the locks from those files and replace them, without the need to do a full IISRESET, taking down other sites on the server. One thing to keep in mind with this file however, make sure you out enough content in it so it is larger than 512 bytes or IE will consider it a 404 and will display the 404 instead of the contents of your app_offline.htm file."

Source

Host in your own country where possible (and practical) as server response time and server location are SEO factors - though not hugely weighted.

However, as .Coms are considered global hosting the US AND UK site on the same US server wouldn't be of huge detriment (in terms of server response time again.) -  if you only want to run one site and split the visitors between /US and /UK subfolders. Remember, you can use Google Webmaster Tools to create Geographic targeting for each sub folder (One for the US sub folder/sub directory and one for the UK for example.)

In a perfect world however I would want to see the sites hosted in the appropriate country as this does help to indicate your target audience (and the obvious server response times I keep mentioning.) Google does allow for those that host out of their own country, hence the geographic targeting option in google webmaster tools.

I think UK users do like to see .Co.Uk at the end of the domain - because they know that generally means they will sell (and ship) to UK users - but we also use global .com stores if re-directed to them (Ebuyer.com for instance.)

• You can always use a .co.uk domain (if you have that too) for marketing only and redirect all traffic to your xyzdomain.com/UK sub folder.

In terms of the ecommerce software, I would (and did) opt for another ecommerce solution altogether:

Interspire Shopping Cart is very good in terms of SEO (The URL structure, H1 tags, meta title, meta description etc are dealt with very well.  We rank number one for a variety of terms using this as the ecommerce solution. (Note this is self hosting) There is a hosted version that interspire are beginning to favour - see www.Bigcommerce.com

Hope that helps!