ive had some fixed bucket seats (in other car) and they are great..... if you find the one meant for your body that is, I really suggest getting the ones with the padding for your bum coz after a while it surprising how hard it feels and also holds you in better.
I wouldnt of thought you would have to remove your back seats unless fitting a 5 or 6 point harness. but someone else can confirm it.
You feel almost every bump from the car in the seats, but it makes u lower and just makes you feel like your part of the car, or least did with me
You can still put a fixed back seat on runners so people may be able to squeeze in the back.......definatly a squeeze!!! lol
hope that helps