Sounds like you got a good start there...
Rocksteady (really Jamaican music in general) is all about 45's. Buy 45's from the years you know they were making rocksteady (68-ish). If your not trying to spend loads of cash just go to ebreggae.com and go to town- tons of rocksteady comps and represses available I like the pressure sounds redbum ball one alot. Other than that buy by labels first- you already picked out a bunch of Coxsone stuff so other studio one related stuff would be an obvious choice. Highnote, treasure isle, merritone and buster are all responsible for tons of great rocksteady so go through that stuff too. Tons of podcasts too, if thats what you want. I like the dancecrasher stuff tim p does or rockashacka's stuff outta japan. If your just looking for album suggestions, I dig buster's ten commandments lp which was put out in the states on rca so not that tough to find.