Help with 3 1/2 week trip to Kenya/Tanzania trip in October
 

I am planning a 5-6 week solo trip to East and South Africa from Sept 25th to Nov 1-5th (flexible).
I plan to visit Kenya, Tanzania, South Africa (10 - 14 days). For now looking for help with the Kenya/Tanzania part of the trip.
I will arrive and depart from Nairobi. I will be doing two stop-overs on my international flight, Nairobi and Johannesburg, and continuing to Singapore.
The following is a rough itinerary. I am at the point now I am struggling with the beat way to organize the safaries. I could do two separate ones as follows. There is also the possibility to do a combined safari which contnures from Masai Mara to the Sarengeti NP and ends in Arusha. In this senario I would not be able to do Tarangire NP.
This is my first safari and I am concerned about a 9-10 day trip rather than breaking up into two with a break in Arusha between them. The other problem might be finding departures on dates that work for me. I am not looking for luxury. Just a comfy bed and good food at the end of the day.

I am very much interested in any and all comments and suggenstions.

Kenya
Nairobi (2N)
Lake Naivasha - Hell's gate NP and/or Longonot NP
6 day safari ex Nairobi (6N)
Amboseli National Park 2N
Lake Nakuru National Park 1N
Masai Mara National Park 3N
Arusha (2N)
4 day safari ex Arusha (4N)
Ngorongoro Crater 1
Tarangire National Park 2
Lake Manyara 1
Arusha (ARK) to Zanzibar $200
Zanzibar (4N)
Zanzibar to Mombasa Flight $150
Mombasa (2N)
Bus to Malinda (Watamu)
Watamu (1N)
- Gede ruins
Malinda to Lamu flight (11:05 - 11:35)
Lamu (2N)
Lamu to Nairobi Flight (150)
Nairobi (1N)
Nairobi to Johannesburg

I think it is good itinerary