Mike,
I am a sales manager with a 5 state territory, and I have been using GTD for the past 2 years. I do not have my customers listed as projects per se because like you, there are too many and my weekly review would get bogged down.
What I think you are asking is how best to review your account base and integrate that process with the GTD methodology. How you track customers in GTD will depend on several factors, including how many "Contexts" you have in your week, how many customer visits per week, are you in the field 80% of the time, etc. For example my contexts include Airports, interminable car rides, hotel stays, customer meetings, and then home office time.
Because I am in the field so often, I place a high premium on having all my data, all the time, in a variety of contexts. That means I live and die by my blackberry. You can try to do some GTD with paper, but as a salesman, you are going to have some sort of electronic database, and from my experience, the guys that just call it early and go as digital as possible with their planning tools come out ahead. I personally use ACT! as a CRM, which I sync to Handheld Contact on my blackberry. I use this only for logging my activities. If I do a customer visit, I log the visit in my BB immediately after. If I have to make a call, I call from Handheld Contact and it gets logged. I make notes if I need to. I send emails from Handheld Contact as well. It all gets logged. At the end of the week during my weekly review I run an activity report in ACT! and there I have all my weekly activities, which is useful to trigger any reminders or follow up tasks I may have missed.
That is just CRM, by the way. The Bare bones of GTD I accomplish through Lotus Notes/Blackberry in a process too convoluted to describe without you thinking I don't need therapy. Suffice it to say I have found what works depending on if I am on the road or in my home office.
As far as the type of items I would put as projects, I would not put "Customer X" as a project because it is not descriptive enough. What do you want your desired outcome to be? Do you want to kill this guy? Take him to lunch? Sell more? Since we are in sales I always kind of assume I am supposed to sell more, but how much more? I might put as a project, "Increase Customer X sales by 15%" (HA! Not this year!) Or, "Get key engineering contact at account Y" if I am trying to break into some place. Usually, projects turn into a list of things I have promised a distributor that I don't exactly know how to do. I might have "Schedule lunch and learn with distributor Z at engineering firm A", etc. How many steps are there in that? What are you going to talk about? Who is going to buy lunch and from where? DO you have your powerpoint tailored and ready to go? Those are your actions.
Depending on the CRM you use, your ideal situation would be to link this project to your customer data, and then link the project to your tasks. ACT! Gets you pretty close, and if you have a standalone version that you can modify, you might even get all the way there. I personally resist that approach because I find the Lotus interface to be more ideal for GTD methodology (Being able to create a Task out of an Email or Calendar Entry, for Example) So to sum up, I have my entire workflow in Lotus/Blackberry, ACT!/Handheld Contact can count as "reference" materials. Projects don't get linked to customer info because the Lotus and ACT! aren't integrated, but I basically know who is who, so I don't worry about it.
I don't know about you, but I find the 80/20 rule definitely applies to my accounts. A while ago I just stopped caring about the bottom 80 percent, because they just seemed to buy at the same level no matter what I did. Such accounts are not worth the brain cells necessary to track, because you might start thinking that there is something for you to do about them, when you should be taking your top customers out for golf and mimosas. I would say the same should apply to your GTD system, don't glut the system with a bunch of dud accounts just because they happen to be on your list. That is too much for anyone to track, and probably your boss doesn't really care that much if you call on them all. Just make your numbers every month and maybe track the important guys as projects with specific goals, and your life will be much sweeter.
Randy