This gets into the realm of opinion pretty fast - it can be shockingly difficult to measure the value of one link. Here are a few of my opinions:

(1) One link is one link. It's rarely the magic pill people want it to be, even from a very authoritative site. I've seen people get a link like this and then wait on their hands for a sudden change in rankings, and it almost never comes. If you're just starting out and you have little or no link profile, a strong link can kick-start you, but I wouldn't pay $750 just to get a link if your site is established (I'm not sure I'd pay it even if your site is new).

(2) DA and PA both matter, and how much each matters can really vary with the situation. Your profile on a deep page of BBB is not an authority=96 link. It will carry weight, but the weight of any given profile could vary a lot.

(3) BBB has gotten a bit more aggressive, IMO, and I suspect Google will devalue these links over time. People tell me that they haven't yet, in this case, but it is, in essence, a paid link. Any day, Google could say "These BBB links are counting too much" and just lower the volume. So, don't put all your eggs in one basket, no matter what you do.

Now, to be fair, your BBB listing does have other value, like using it as a trust signal. The business case for spending the money goes beyond SEO, and that's a decision you have to make for yourself. If 100% of your interest in the listing is for a followed link, though, I personally would spend the money elsewhere.

It is probably best to create separate profiles in Google Webmaster Tools, because then you can target the sub-domains to the countries in question. At that point, you could also set up separate sitemaps. It'll give you a cleaner view of how each sub-domain is indexed and ranking.

I'm not sure I understand (2) - why wouldn't you include those pages in the sitemap?

There's no perfect answer. Canonical tags would keep the sub-domains from ranking, in many cases. The cross-TLD stuff is weird, though - Google can, in some cases, ignore the canonical if they think that one sub-domain is more appropriate for the country/ccTLD the searcher is using.

Sub-domains can be tricky in and of themselves, unfortunately, because they sometimes fragment and don't pass link "juice" fully to the root domain. I generally still think sub-folders are better for cases like this, but obviously that would be a big change (and potentially risky).

You could try the rel="alternate" hreflang tags. They're similar to canonical (a bit weaker), but basically are designed to handle the same content in different languages and regions:

http://support.google.com/webmasters/bin/answer.py?hl=en&answer=189077

They're basically designed for exactly this problem. You can set the root domain to "en-US", the UK sub-domain to "en-UK", etc. I've heard generally good things, and they're low-risk, but you have to try it and see. They can be a little tricky to implement properly.

For all practical purposes, Google doesn't seem to index pages where it recognizes the canonical as legitimate. You won't find them in a "site:" query, "cache:" command, etc. Google may call that a "filter", but once it's reached that point, the URL is as good as de-indexed. There may be subtle, technical distinctions, but the end result is virtually the same.

As Google starts to factor in user behavior, like CTR, this kind of thing may be even more important. I think it's a very small piece of the ranking puzzle right now, but I'd expect it to grow in the coming years. Google wants to rank the page that best answers the question, ultimately.

This is a very complex issue, but I think Jonathan's summed it up pretty well. Generally, home pages collect a lot of the "mass" of inbound links, and so they can overpower other pages. On the other hand, deep pages are easier to target to specific keywords and sometimes have targeted anchor text. I've seen cases where someone wanted the home-page to rank, but a deep page was ranking, and I've seen the opposite.

Rand wrote about that general problem here:

http://www.seomoz.org/blog/wrong-page-ranking-in-the-results-6-common-causes-5-solutions

While it's not exactly what you're asking, it covers the general logic of why one page might win over another.