The number plate is a must as a mate has been done before for not having had it on the rear of the rack.
Something like that Thule will work fine.
I take it you are aiming for one that the bikes sit on by the wheels rather than hang from the top tube? (understandable if they are mountain bikes)
Know of a few with those Yakima brand ones, or other similar styles, they all do the same thing.
Personally i just use some 20-25 year old A frame style rack.
But if you want to really look into another style, check out a brand called "Dirty Possum"