Tanzania + Kenya combination

Hi. I haven't been to those specific countries but, in addition to the great insights from travellers here, I've found the Safari Talk forums to be a good resource for the wildlife viewing trips I've taken. https://www.safaritalk.net

We have used Africa Adventure Consultants twice to book our trips and found them wonderful to work with.
https://adventuresinafrica.com/

Three years ago my wife and I as well and my son and his friend took a wonderful safari during The Great Migration (early August) with Good Earth Tours. It was great.
We flew into Nairobi, did a tour of that city, then the next day started our safari. It was about 1/3 in Kenya and 2/3 in Tanzania. We had different guide/drivers in each country (required by the law of each country).
BE SURE to go in early August and enjoy the great migration, it is fantastic.

The four of us were in a large off road vehicle with room for our luggage in the back. Not sure about hiking, we were told when we could exit the vehicle (in the game preserves, it is generally not safe to leave your vehicle). The most dangerous animals are the Water buffalos and Lions. They more very fast.

Our guide was able to get us extremely close to prides of lions, elephants, and other wildlife. The safari tour was about $4200 per person for a total of 9-10 days.

One important bit of advice I can offer is to choose a travel l can that includes stays in private conservancies,r other than national parks, where you might share your sightings with 20 or 30 other vehicles, all crowding around one lion. It costs more to stay in a conservancy but the experience is like night and day as compared to staying inside a national park.

I'd also advise using a safari planner to customize an itinerary for you and your group, rather than taking a tour.

While on our Good Earth Tours Safari, we did find that frequently when wildlife was found ( almost always with MANY such animals) several other vehicles showed up. Our driver/guide communicated with others, so when wildlife was found, more vehicles could come to see them. We never felt crowded because of the other vehicles.

During the great migration we saw several sites with literally hundreds or thousands of Wildebeasts that were in the process of the great migration.
Also, when we saw lions, we usually saw many lions together.
Leopards and Cheetahs were usually alone.
Also, we saw massive numbers of zebras and gazelles of different sizes.

I'd much prefer to be in a pace where there were not other vehicles crowding around the animals, whether it's one lion or a family of cheetah. That while system of having the guides calling other vehicles to the spot results in the kinds of crowds that, unfortunately, the Mara has become notorious for.

https://www.nytimes.com/2023/01/04/travel/masai-mara-safari-overcrowding.html?unlocked_article_code=1.GlE.NmRf.h06Shgb4KY0H&smid=url-share

When you say you want to hike Kilimanjaro or Kenya, do you mean hike/climb to the summit? We climbed Kili 20 years ago in our 50's and while not technically difficult, it required a lot of planning, training and stamina. It is difficult to train for the altitude, but that is the singlemost factor that limits folks from summiting. Then there is the route to choose - there are several options, each with benefits and limitations. You stand the most chance of summiting if you plan on 5-8 days on the mountain. Since you cannot hike alone, you need to investigate a company that will assist. Since my experience is 20 years old, I can't recommend a current one. My husband and I were the only climbers/hikers/trekkers, whatever you want to call it! but we had a support team of 12-15 people. It was an exhilarating experience, one which I highly recommend, especially if you enjoy hiking, but it requires it's own organizing. We combined the climb with safaris in the Serengeti, Lake Manyara and Tarangire with a few days on the beach in Zanzibar afterwards to recuperate.

We found the best of our Kenya and Tanzania safari was in the Serengeti in Tanzania, rather than the Masa Mari in Kenya.

Not matter which country you are visiting, the national parks are known for overcrowding, with many vehicles at animal sightings. Best to stay in a private conservancy, although that might be more expensive. Private conservancies are managed by the local people, and you can do night drives and go off the main roads in pursuit of game. They are usually located adjacent to the national parks.

https://kenyatanzaniasafari.com/private-conservancy-safaris-kenya-tanzania/

A safari planner can assist you with all this..

I wonder if the OP can share what their approximate per person daily budget is for this safari. Given that the daily park fees per person for the Mara is $200 for a 12 hour period during the great migration, the cost of this safari in a private conservancy is going to be very high. We need to know what is most important to the OP, is it private game viewing, seeing the great migration with others crowding around, and if cost is not an issue.

I agree, Arnold. I am pressing hard here for a stay in the conservancies but staying there can be much more expensive. And we know nothing bout the OP's budget.

But even so, I think the stay in a private conservancy in Tanzania is about half the cost of staying in a prime lodge in Botswana. (You can see where my rationalization is leading me here...!)

Also, if the OP is planning this for a few months from now, time is running short.