Redvanes, I don’t live in AK and have only shot one moose, so take this for what it’s worth. However, I’ve been fortunate to shoot a fair number of animals that take equivalent power as does a moose, to kill reliably, given any reasonable shot. Sounds like your moose hunt is a once in a lifetime experience, so having a rifle chambered for a cartridge that will allow you to take any reasonable shot presented is probably a good idea.
I’m an unabashed rifle loony so have had several rifles in both 300WM and 300RUM. I like both cartridges quite a bit - they’ll both kill a moose if you place a well constructed bullet into the vitals. I shot my moose with a 325WSM with a 200 grain Nosler PT, because it was a new cartridge at the time, in a SS-synthetic rifle, perfect for the AK weather you’ll likely find too. Ballistically, the 325WSM cartridge is identical to the 300WM and WSM.
For a number of years now, however, when I need a rifle in the 300 mag class, my choice is most frequently a SA 300WSM with 180 Nosler Partitions. I am very familiar with the rifle, confident I can shoot it accurately as far as I need. It’s never let me down. The rifle is light - I carry it a lot more on every hunt than I shoot it - something I wouldn’t underestimate. You might consider a similar option.
To answer your original question, if you like it go for a 300 mag - the RUM is probably more than you need and the ammo is expensive and hard to find - practice with it, and enjoy your hunt. SS in a synthetic stock is a great idea. As you already heard, skip the muzzle brake, it’s an unnecessary hassle. If you practice enough, recoil won’t be an issue.
