I dunno how i missed this thread so i'm sorry for such a late reply.
1) You shouldn't have any problem finding people to paddle with, there are usually always paddlers around. If not, & if solo river running is your thing, its not so bad. Although i would leave widowmaker and the like alone until you get some people to paddle with.
2) You should be able to sell your boat, the only issue here is that you probably won't get as higher price as you'd hope. There are many local paddlers always looking for boats but they are not the wealthiest people so don't expect do fetch a high price for it. Maybe Jamie (from Kayakthenile.com would be keen?)
3) Jamie does have a range of boats to choose from, albeit it is dominated by Fluid boats - which doesn't bother me at least
4) In terms of the Zam your best bet is to check flysaa.com for flights between Entebbe and Livingstone. However, in January the Zambezi levels are a bit high and it can be very scary at those levels if you're not used to big volume. If i were i'd save my cash for a another trip and head to the Zam separtely in the 2nd half of the year.
Hope that helps out a bit.
Scotty R