Count the useful wildlife time, rather than the names on the itinerary. Arrival, departure and changes of camp all affect what a stay actually gives you.
Tarangire often appears near the beginning of a northern safari. That is a reason to give it attention, rather than hurry through on the way to somewhere else.
The coast can be a beautiful change of pace after safari. It works best when the beach chapter is part of the first plan, with enough time to feel different.