As above lots of good points. Terrain can make a lot of difference, each has its pros and cons.
It 'IS' possible though, Iv stalked and killed Turkey, Whitetail and Elk in the US, but have no experience with the others in the USA, so can't compare them, but on a whole Africa is bit harder I would say, a lot more predators and the game is really wired most of the time, they don't drop their guard much.
Iv killed most of the African plains game available to me, walk and stalk, and to be honest there are not many that are easier then the others.
Of the Above, Zebra are hard, your best odds are when they are moving, they will form a line and if you can predict where they are going and get there fast enough you can have them come past you.
Kudu, you'l want to find a bull by himself in the ideal situation feeding, if there are a herd of kudu cows, its 10x harder. Patience is the key with the Kudu.
Warthog you can stalk if you catch them feeding, better if in long grass, as above reactions are lightning fast!
Wildebeest are hard, again try find a mature lone bull, wildebeest are territorial and will have middens and dust baths in their territory, if undisturbed they will also bed in the same small area for days, they will often bed by midday out of the heat, that can be a good time to try for a stalk.
For the most part camo is camo. I like to have a lighter brown and a darker green options to suit the bush Im most likely to be hunting. Covering your face it critical, I use face paint.
leather boots with flat soles are critical.