Hi; It depends what kind of music you're interested in.
If you want to play the baroque school, then there
are many small organs to choose from and they
don't required too much RAM. I can only speak
for Windows---7 pro 64bit is best. If you want something
grander or bigger, then you need at least 8Gig RAM.
There are several sample sets converted from Hauptwerk
to GO, but they take a lot of RAM. If you go to some of the
AGO extended samples available for Grand Orgue, then
the 8 gig RAM will work. Just depends on what you want to
play. If you have a Viscount, then I assume you will not
be playing through headphones, so you need speakers and
an amp for the main output, and possibly a powered subwoofer.
I use generic, over the internet, usb/MIDI cables that about $5-6 each.
Are in you in the US or Europe? Michael will probably have some ideas, also.
If you are a proficient player, you may want to consider OMNI when it
is put on this website. All the best, Ken Barta