Congrats... You will get much advice here, and many different suggestions. This is my thoughts.
As you dont have a big caliber yet, then a 375H&H is best for this first hunt, with a 1-4 or 1.5-6 type scope that MUST have lots of eye relief (eg Leopold). Use QD mounts if you can, and check the open sights also. A scoped 375 is great for that Kudu or Bushbuck that temps you and the PH. Personally I love and use big calibers, but also I dont like sighting in and bench practice, for this reason I suggest a Kickeze or Limbsaver recoil pad to be fitted, and the Length of Pull changed to suit what is comfortable for you on your other rifles. I like Hornady factory ammo for its reasonable price for Dangerous gane, and solid and softs are tough and regulate good. In 375H&H I like CZ rifles because they take 5 in the mag, and action is not too big. The weight is a touch heavier than others which absorbs recoil a bit more. Winchester, Remington, Kimber, and Sako (and others) all do the job, and you probably already have a favorite brand. When sighting in and practicing you can use the cheapest ammo first, (then fine tune to you Hunt ammo later). Very carefully bore sight first to save getting kicked more, then fire at 50yds on a big target, adjust, then move to 1ooyds, set 2" high at 100yds, for about 200zero. Next session at the range can now be more fun, fire a couple off the bench, a couple leaning tree position, and a couple kneeling. Then set some target at varying distances, and shoot at 50, then fast offhand follow up at 75, 100, 125. You will have fun doing this, and high chance this is what will happen in the bush anyway. All during your practice, start with ammo in your leather cartridge slip on your belt, set either middle or slight opposite side to your normal slung over shoulder carry side (to be immediately accessible, and not scratch rifle). Then every time you need bullets, load FROM your slip. Another practice session can include 3 water bottles set at 20, 12 and 8yards... look away and have you mate yell "charge" face and shoot 3 perfect shots furthest to closest... if you rush its a disaster. Shoot fast but aim and squeeze.. this may save your life. Remember the only thing that will reliably stop a charge is a brain shot or a spine shot.. so you must be able to hit an Orange size at each of these distance. but if for example your shot goes high, hopefully its into the spine... Practice, practice practice. Also get a Past recoil shoulder pad for practice. If you dont like recoil and you wish to reload, then you can make a mild load for practice. But once you start reloading then you have another nice problem which bullet to select.
This sounds about as much fun, as me and my mate preparing for our Mozambique Cape Buffalo hunt in 7 weeks time. My Rigby 416 rigby and me are now fine tuned, and Andrews 500 has been ready for years...!!
Oh yes practice some more, especially loading into mag while looking away and moving..!! Keep another plastic slip of 5 in you right pocket, and give your PH a slip of 5 for his left pocket, just in case.
Practice, practice again, and even carrying the rifle around at home a bit (with bolt removed) gets you used to the carry, handling and balance of this new heavier rifle. Take your hunt and practice seriously, as dangerous game hunting can go wrong, and you may have to save yourself or the PH. Even other animals wounded and/or cornered can charge.