I agree with everything here. It is pretty much the same the world over. A local trekking company will be far less expensive, though it may be a little rougher. I was with African Walking.
I'll add a bit on the post-climb safari. If you safari on the Tanzanian side, it should be the Serenghetti. My friends that have done the closer areas were not pleased with the wildlife.
I did Amboseli on the Kenyan side. Very nice, though the hut in the N.P. was $399.00 per night. It however included the walks and wildlife viewing rides.
If you're from the US, you'll need a Kenyan single entry visa and a Tanzanian multiple to do this.
The Land Rover "Taxi" cost me $300.00 from Kili to Amboselli. It was an adventure in itself and well worth the money. You have to take the long way around, even though you can see Kili from Amobseli.