@importa, just to add to what Mzee Njung'e said...fuel is cheaper in Malaba/Busia...better still, the halfway point is either Kisumu (Busia) or Eldoret...well say Webuye (Malaba)...fuel up there...
I'd suggest leave Nbi with half a tank...if your tank is 60 litres, think of it as one child passenger to go with full tank...for 350 km...adds to consumption....so leave with half tank...it should get you to the aforementioned towns....then gas up again...this time full tank...that should take you to Kampala and allow some running around and perhaps get you halfway back to the border, where you can gas up just enough to cross over into Kenya.
Busia/malaba to Kampala is 210 km....but the last 20 km feels like 300 km owing to traffic and caveat...Ugandans are not the best drivers on earth...be wary...expect turn signals after they start turning....while they are poor drivers, they love speed.
Watch out for speed traps near Bugiri...this is abt 90km from the border. When approaching every small township...slow down to 50km...the traffic cops there tend to be rather stone faced and will slap you with an on the spot fine of Ushs 300,000 (divide by 28...)
You don;t need a road licence, however you must have at least TPO insurance which costs abt Kshs 3000 for four months cover (sorry, not two week insurance like we have here). You can get this at the border. BTW, we extra wary of "agents" who want to help you cross (Pls look for another discussion somewhere in Wazua on a similar topic which covers this issue rather thoroughly).
I'll also be pointing my old bomber westward mid-August...
Via con dios...