The 120 comes with a much better cartridge than it used to, so you needn't worry about excessive record wear. If you want to upgrade the cartridge anyway, you need to worry about proper installation/alignment. Its doable, but can be a little intimidating for a newbie. You might consider buying from a turntable specialist (Needle Doctor, LPGear, etc.), which will install the cart for you—but at a price, of course. A 120 with an M97 installed will run you over $400. Since you're just starting out, I'd stick with the stock cartridge.
As for the accessories, I'd skip the gauge and the Audioquest brush. You'll be able to balance the cartridge well enough, and the kit comes with its own brush.
If you can't explain how it works, you can't say it doesn't.—The High-End Creed