About the easiest way to cut a straight edge on rough stock is to build a simple jig I'll attempt to accurately descibe. Get a piece plywood about 6-8" inches wide (straight/parallel edges) and maybe 8' long. Screw a stop block across the trailing end of the plywood - check that it's 90 degrees to the plywood edges. Then screw the piece to be cut onto the plywood at the ends of the piece to be cut, with one end against the stop block. Just leave one edge of the plywood jig clear so it can be run against the fence on the tablesaw. Then set the fence at a width that will catch all of the edge of the piece to be cut, and let 'er rip. One straight edge in no time. (If I haven't clearly described this, I think I can find a thread somewhere that I know has pictures of it.)
Making the jump from S4S to RS really calls for both a jointer and planer. Trying to do it with only one can be done, but it requires a lot of fiddling around to accomplish. A planer CAN be used as a jointer to produce one flat surface, but that calls for another jig system. I have a 6" jointer, but I can use the planer to do wider stuff.
The best part of using RS is that some of the S4S 3/4 lumber actually needs planing, jointin to get good material, so you end up with stock thinner than 3/4, which is kinda flimsy. I've gotten 15/16ths or 7/8 lumber from 1" RS and it makes for sturdier construction.