My go to gun is my 30-06. You can find a good selection of cartridge for deers up to big games like bears and elks. I have a Savage but I also like the Tikka. 3-9x40 is a good choice of scope for this type of gun. The .308 will work well for Moose (they are thin skinned animals) but might be a little light on bears.

For your African trip I suggest you check with your outfitter when you get closer to your departure date. Some of them will provide you with the gun you will need. That will save you the expenses of buying a gun just for that purpose. Of course you will have to practice with the big gun before you go so you might end up buying a big gun after all.