Just earlier today I cleaned up my favorites folder with all the LLs I've submitted to over the past 2 years (100s), and, not surprisingly, quite a few of them have gone belly up. You need to be prepared for a lot of work for little pay for a long while. After having a LL for close to 2 years I dare say that I wouldn't quit my day job if I had one.
When you buy a script don't look at price. If you plan on staying in business for the long haul, the cost of the right script is negligible. I recommend taking a look at
Dragon List before you make any decisions. While XPL certainly is a capable script I feel that DL is more flexible and a lot easier to customize with your own design (I own both XPL and DL).
As far as number of categories is concerned I used to agree with Fonz, but I'm starting to wonder if it's better to go for a larger number. You can always fill up the cats that don't get many submits with sponsor hosted material and just let them age and gain PR right from the get-go.
If you haven't done so already, read
Preacher's thread on his experience as a fresh LL owner. Lots of good info there. Best of luck!