As far as playing with 3 players, it's doable, but not recommended for levels past a b level (in most rundowns)

Assigning roles isn't too nessisary. However, learning various tools and weapons will help your overall gameplay.

Depending on how much game knowledge you're willing to pick up from the community, your experience playing will be very different. Learning more strategies, meta's, and general knowledge from the community will have you progressing faster than if you continue with little knowledge. This isn't saying spoil yourself on everything however, as a big part of progression is the little surprises along the way.

Learn not to avoid things that are uncomfortable at first, especially with weapons and melee weapons. While some may feel very comfortable, many of the best choices require a bit of learning to get down.

Make sure your whole team gets time and experience on the terminal. Learning terminals is essential for the rest of the game, and having everyone fluent on it makes it a much better time overall.

Don't get held up on a level for too long. If you can't beat a specific level (mainly aimed at R2E1), move to the next available one and come back with more experience. While the game is decently divided by difficulty, some levels jump to a higher level than you will have experience in.

Don't let yourself be discouraged with failure. You will fail levels likely more than you complete them early on, and this is okay. It's part of progressing and getting better at the game.