1) He means literally make one "World of Warcraft" program folder per account.

2) It is true that Visa fraud prevention called me when I bought 4 online battlechests. It might be easier to get the boxed key from a local store, yes. Assuming they match the online price. With my account, at least, all I had to do was verify a few account details and tell them that the charges were legit and it was fune

3) What Asterix did was not RAF link using his main account, but using a second one. See his diagram up there, b>c>d>e, but A is separate. most people would prefer that A not be separate because you don't get as many level grants that way. Also, since you said your goal is to transfer your toons to one account after leveling, you definitely want those granted levels. I would even recommend going a>b>e and a>c>d. That way, you still get all the RAF bonuses, but you get twice as many levels to grant to account A(because both B and C are linked to it).

4. Yes, ISBoxer will do that automatically. I have one world of warcraft folder on my hard drive, and ISBoxer handles getting everything launched and keeping all my character configs separate from each other. Personally, I don't have enough good things to say about ISBoxer. It's great. There are also a ton of videos and tutorials related to setting it up. For just boosting, it requires next to no set up. You would just go through the quick setup wizard and enter your toon names. That's basically it, though there are many, many other features that you wouldn't be using if you use it strictly for boosting.