youre about right. you can run 1 fixed one recliner, but the rear seats still must be removed, the reason is passenger access/ability to get out of the car in an emergency.
the seats also need to be ADR compliant. to my knowledge this is the velo bottom mount ones, and some of the chinese brands sold at big auto parts places.
rails can be modified stock which any one who does mod plates can pass. if theyre scratch built, you will need an engineers report. id say technically that would go for bride/copy rails, but i would guess most mod plate guys would pass them.