Congratulations on the trip, I am very jealous.
1. Video is not the K5's strong area. Depending on how good you want the video to be... I would probably just bring an HD recorder.
2. I personally would bring the grip if I were bringing some heavy lenses. I.E. DA*'s, large zooms, etc. But if you have lighter lenses, then I think I would leave it at home and pack other items.
3. A couple zooms completely do away with primes.... but depending on what you want to shoot, primes might be the best option
4. I always shoot JPEG
5. I would personally bring what I have for memory, 4 16Gb cards. Ideally, for myself, I would buy some fancy 8Gb cards, probably 6 of those and be happy.... but then I would have to buy new cards. But I would make sure to back them up on a computer every night if possibly.
I think what we need to know from you though is: What lenses do you currently have/plan on taking? What animals are you going to be seeing? Are you in a vehicle all day?