You may wish to peruse the offerings on the Bogen Imaging web site:
http://www.bogenimaging.us/
As for the quick-connect plate, I've not seen the RC-4, but I have both RC-2 and RC-0 plates on my various tripods. The RC-0 is the larger hexagon-shaped plate like on your 3047, while the RC-2 is a smaller rectangular plate. I believe that the 2 is a bit lighter but can mount only one way. On the other hand, the 0's hex shape allows more mounting positions FWIW. Don't know a thing about the 4, but it also looks very sturdy.
I believe that the 468 & 490 heads are pretty good - I have an old predecessor to the 468 and it's a very sturdy old thing. Not nearly as nice as the newer heads (no teflon, odd release levers, etc.), but it will hold a good deal of weight. The 488 is probably a better match capacity-wise with the 3021 legs, but there's no law that says you can't have the better head on those legs.