Wireless Adapter only works with games programed to work with it, so no R/S.
GBA Pokemon games are completely incompatable with older GB games. I don't think there was any way around it anyway, since they run on different processors.
Yes, GBASP plays all games for GB, GBC, and GBA (except Kirby's Tilt 'n Tumble, which has an orientation sensor designed to be pointed up rather than GBASP's down), because GBA and GBASP have the GBC's processor built in. I don't think the same is true of GBAmicro, though.