Flora and fauna
There are many different animals, including monkeys, in the reserve. However, unless you are lucky you won't see them.
The road is dirt, and very bad. It might look a short way on the map, but it takes a while. Buses do go to the village just outside the reserve, or you could take a 4x4 vehicle. But, be wary during the rainy season, you could easily get stuck for days.
Fees and permits
You are required to pay a park fee, hire a nature guard (he or she will have a gun), and probably a guide as well. Total should be around 10000 to 15000 CFA for all three.
You'll be walking, there are no other transport options in the reserve.
Pygmy villages, you could pay to see a traditional dance.
There isn't much to buy, or many options.
Eat and drink
Best to take your own food if picky. Some of the locals may cook for you if you ask (~3000 CFA).
Your two options are camping or staying in the village just outside the reserve.
It's best to go with a guide who knows the area and can advise on all the above. Contact a tour company (e.g. in Yaoundé).