USDollars or Ksh?

We are off to Kenya in a few days. Nairobi, then 3 nights safari and train down to Mombassa. 5 nights r&r Diani Beach. Struggling to decide whether we order Kenyan currency or USD. Most of our spending will be tips and drinks at the hotels. The safari is a 3 night stay - how much should we put aside for the tips for that? We don’t want to cause offence but then again don’t want to give “silly money”. We will obviously reward excellent service. Any advice appreciacted. We are getting very excited!