Its basically very easy - connect the soundcard with the midicables to the keybaord and then, as you said, connect the output of the roland with the input of your mixer/soundcard. Depending on the software you use this might work right away or you might have to select the propper midi-device first (depending on soundcard and software).

yOu need to use a programm(sequencer) that sends midi-signals ot the keyboard (of course).

A midi-module is basically nothing more than a keyboard without keys. you´ll get most keyboards as soundmodules too - i bet there is a Roland EP97 sound-module out there.

oooor you get logic audio and there you have heaps of sound-stuff included.