Ha. Ha. I've been answering my own questions too. We used miles and have flight in/out of JNB, so am dealing with similar logistics. I already have safari booked. Intra/Inter Africa flights are expensive and can't usually be booked with miles. My best at your questions...
1 - I'd guess, although there are some weird late night flights
2 - yes
3 - would have to find out what kind of connections available, just heard back from TO today about a Serengeti - DAR flight that I couldn't find
4 - yes, do ZNZ after Safari if flying out of DAR
In Tanzania, most of the Safaris are overland with one operator and Land Cruiser / driver. If you contact them they will be able to help with logistics and availability (which might be limited for June). How much time do you have?