So I built a single speed from a huffy howler mountain bike a couple of months ago, not the best idea but the bike was free and needed work anyway. It's super sketchy since a lot of the parts were rusty and it was just sitting for a long time but I got it to work, I just want to make it better. I will be taking apart the crankset for some much needed maintenance but I need a better gear ratio so I would like to be able to try new chain rings. If I buy a used crankset, just the crank arms and chainrings, will that work with my bike? or do I need to buy one with the bottom bracket too? will any crank remover tool work on any bike? Another question I have is that since I have a full suspension on this bike, should use have a chain tensioner?

This is what it looks like right now. I'm planning on getting bullhorns, new pedals with straps, new seat, maybe some led strips for night riding and I'm going to paint it. This bike is purely for fun which is why I don't care that it looks so weird.