First of all, welcome Chrisduk to HC forum.
Now coming to your questions, I'll be replying in same order as questions are asked:
Yes, you can move/migrate all these servers into one big cluster managed by Hosting Controller. The sites and users will be migrated in step-by-step process which will take some time but will elimenate any chance of error.
Now coming to your migration tool questions: If you run HC migration utility, it will move selected/all users/website into HC panel and currently there is no transition stage where you keep migrated domains in inactive/passive mode for testing - once the migration is complete, the selected websites are moved in HC. Yes, migration manages the FTP account anc currently it does not support migration from WebSitePanel to Hosting Controller for Hyper-V module.
On General Questions: Yes, WHMCS is fully supported in HC8, build-11 and for multi-cluster support will be available in upcoming build. In HC8, ability to create reseller under reseller is not available. Yes, you can disable any service including Billing or domain registration globally. We've a rebuild utility under the name of rebuildXpress,
http://www.hostingcontroller.com/english/products/rebuildXpress/Features.html and lot of more features related to RBX are coming in next builds and version.
Now questions related to Module: Hyper-V module doesn't support bandwidth monitoring (and currently Hyper-V itself doesn't provide such support). The RAM can be assigned to specific plan but could you explain this dynamic RAM concept? Configuring network adapters feature is available though Sysprep (Generalized VHD) support will be available in our upcoming builds. kindly refer to this link which explains some of your questions related to Hyper-V module,
http://www.hostingcontroller.com/english/products/Virtualization-Automation-Solution/docs.html .
And to the similarities of online content, I am not sure why is this? or maybe we've a new technical writer from DNP Canadian office as our office isn't far from it

Don't worry, we've skilled team who take cares all documentations.
To your questions on Support/Development/Update: If the bug or reported issue is a show-stopper then fix will be available immediately otherwise in next build. Similarly, we're very open to new requirements and suggestion, generally the response time is quick on feature requests as well. Big, big plans for Hosting Controller in year 2012, 13 and followings... Of course, HC9 will be coming with lots of exciting features. Once you become HC valued customer, we would love to share our roadmap with you. The average response time on Support is less than 4 hours and if you're a priority customers then response time is much faster too. Better, test it yourself by sending email. SSL is not configured on online demo but test it locally or on test environment - it works flawlessly.
And I will suggest if you communicate with us through email (ticketing system) - the response will be quick. Moreover, our team is available 24/7 to answers your sales or technical queries.