I was reading a singlespeed conversion guide and I thought simply i had to remove the shimano freewheel from the hub, and put in a bmx freewheel. Then no more brakes, no more shifting. Bmx freewheels allow coasting, right? If they allow coasting, how do you brake with a single speed bike, do you have to keep brakes on the bike? Then if i dont want brakes, I need to go fixed gear? so confused...

You need brakes. Fixed or free. Stopping without brakes if you have a freewheel is impossible unless you are Fred Flintstone. Stopping without brakes fixed gear is about as effective as stopping your car by downshifting (the same principal, actually).

What about coaster brake hubs, could I just get one of them and be set, coast, brake, no lines running on the bike, no shifters, no hand brakes, just backpeddle and brake, or coast when I want, or pedal, This sounds like heaven.

Absolutely, that's the glory of coaster brakes. They sound like they're exactly what you want.

Though, if you're descending mountains, apparently you'll not want a coaster brake - they melt. No worries in normal use.

And you only need brakes on your bike if you have a freewheel.

Okay, then the question is, where do I find a single speed coaster brake hub to fit 126mm rear spacing? Because of the coaster brake, am I going to have to find a coaster brake hub exactly 126mm wide? I am very excited about this

Uh, that's like a hard question that requires actual knowlege to answer.
Can't help you there.