Hi Oli,
Hope this message finds you in time, if not, I appologies, but I have not been able to get online.
Yes, that's a good plan. I stayed at the following: Keytundu which is across the street from Mount Meru Tracking, which I did tracking with and I heard they are good for safari, but you have others listed above as well. Also Ujamaa hotel is great, but not as close to center of now.
Tips for Safari, take your time and shop around. Even good companies sometimes put you with another company. Be careful of any company that suggest a walking safari.