Agree with the 270gr --but I would use Swift A-Frames--hard enough to use on Buffalo and yet will not blow up the small stuff.. I have taken really small stuff with 400GR A-Frames.. little damage--like hitting them with a solid..

IF, plains game only, agree, you do not need a 375... 7MM or 300Win is better as shots can be longer in Namibia.. more so that typical in Zim or similar areas.. Having said that, even if going for PG only, when I am in Zim I take a minimum of .375 as you never show who shows up at the party..

In terms of equipment.. good sun hat, and QUIET shoes.. bring a day pack--you will not be carrying it while hunting .. and they will also be carrying the water.. and your rifle if you wish, which I never do.. again, want to protect myself if need be, not running after a guy to get my rifle...

Sun block is a necessity ..depending on when you go, can be cool mornings but by 10 its getting warm.. I wore only shorts on all of my hunts there.. and will do so again when I go back.. had sand covers for my boots to stop that from entering my shoes.. VERY helpful.. see link below..
https://www.shakariconnection.com/african-hunting-gaiters.html

EYE PROTECTION.. lots of long sharp thistle, etc .. can take an eye in an instant.. beware..
clothing.. wear something the brush cant grab so easily--cotton sucks..do not bring it

As stated, could go on and on for the next 2 days..keep it as simple as you can..

Will need medication and shots..depending on the area. Malaria area ???