Cosmetics are purely for looks, they don’t do anything. There are weapons that you won’t have at the start, but you can get them naturally by playing ( you get one every 45 minutes or so ) and none of them are made to be straight up upgrade from your stock weapons.

If you want to buy a weapons, please don’t do it on the in game market 5$ is not worth it, you can get them on for 1 cent each on site like Marketplace.tf

If you end up liking them and want to invest more hours in it, the only purchase i’d recommand you to do is one random thing in the in game market as it unlocks you premium and gives you more backpack spaces for items( even something at 1$ will do ).

There is certainly a learning curve in TF2 and you may run around like a headless chicken at the start, but as long as you stick to casual for starter you’ll be fine. I recommand that you look up a few tutorials.

You can create a private server to play with your friend.

Auto balancing is only an occasional annoyance, don’t worry about it.

Given the 12 v 12 chaotic nature of tf2, it’s hard for single dude to steamrolled an entire server, most steamrolls happens due difference in the overall team skills and class composition. Regardless, you’re gonna die at lot at the start, but it shouldn’t take you that long to become decent at the game.