I think, from last year (dont quote me).. That the seats and harnesses have to be FIA, but dont have to be in date as long as they are in good condition. Certainly last year, my SPG's were out of date and it was fine, but my harnesses were in date. They were also 4 point.
Door bars, again i think that single is OK provided you havent modified the doors them selves, or have FRP doors etc. If youve removed the inner skin then you need twin bars. Or just re-fit the door cards

I dont know about the passenger side rules.
I have single door bars driver and passenger.