WOW Refugee here.

One thing about WOW that was difficult for me was the need for lots of friends to progress in the game. Is that sort of thing necessary here? Do I need to have 5 or more good friends playing or will I be able to fully experience the game and achievements on my own?

No.

Many zones will autogroup you upon entering, but you can disable this.

You should join a Fleet so you do have access to help when needed, but it is not required.

You could solo this whole game if you wanted, but you would not be able to do the content designed for groups.

This game is pretty solo friendly...however it's also built to try and get you into teams. It has an option called open teaming (turned on by default) that automatically dros you into teams with other players working on the same missions as you.

When you're not playing with other players though, you get to command your bridge officers as henchmen. They can be geared and have their abilities customized as well. The game also scales mission difficulty based on the number of players.