Hi Turkey! (that's a fun username for this weekend for us folks in the USA!)
I saw this question a couple of days ago and just noticed that no one has responded so I'm jumping in. I am just going to first answer each question one at a time:
1.) Should I be considering the homepage url anchor text as a branded link anchor?
Yes, definitely.
2.) Should the brand % just be 'pure brand' anchor text?
Not necessarily. That is going to depend on how you handle your organization based on these next questions.
3.) Should it contain partial brand + KWD data?
Yes, definitely.
4.) Should it comprise of all of the above elements?
Yes, definitely.
5.) Should I divvy up / segment partial brand, pure brand, brand + kwd, citations etc into new sub categories....
Your last question I would take on a case by case basis depending on the depth and breadth of the brand itself, the size of the website, number of SKUs (if e-commerce), etc. If you have a brand like "Chevrolet," for example, of course you are going to have categorized subrands like "Corvette" etc. On the other hand if your brand is a smaller family-run business, maybe doing business in a particular location, you might be able to consolidate all of your "branded" terms to simply be anything that includes the brand name + anything else (including the URL). This will also depend on your resources. Obviously if you have a smaller company with limited resources, breaking all your branded terms into subcategories may just be too much to manage. Again that will be a decision dependent on your business size and business model.
I hope that helps get the discussion started! Good luch,
Dana