Re O/P
I'd go with see how SS6.3 goes before starting new version of RC/RR.
(bug fixes good though.)
simple modding - a few files for example should be easy enough but a big mod is going to be another matter.
also I think we can expect some sort of combined bugfix for SS6.3 once the report backs from the public release are pulled together.
I suspect that the audience for SS6.3 is not the same as perhaps a year or two back.
My impression is that many of the newer players are younger and want a zippier, less demanding game?
(on a personal note after playing with the RozMod/ SS RC6.2.4/ RC/RR combo with PSFs, all towns etc the SS6.3 map seems empty, the time scale all wrong (much prefer 2TPY)
and the rebels and mercs need sorting out. But there are some good touches - rebel merchants etc and the new campaign map is much better.)
Have yet to be convinced on the new installer but that may just be an oldie's resistance to change.