hsv,
Hi and welcome to the "Homebuild Cockpits Forum."
Answering your first question...........
MOST people run external gauge programs on separate networked PC's to keep the "load" off of the main flight sim PC. Unless you have a bear of a machine, you likely need all the horsepower you can get to deal with just running fs2004 or (particularly) FSX.
It IS possible to share some instruments.... on a second monitor from a single PC.... or even MORE monitors with multiple graphics cards ........... but few find success with that approach.
The good news is that the PCs to run most add on panels / gauges are pretty minimal. My PFD (along with some FSXpand gauges are running on a 100 mbit switched network on a 300MHX Pentium II.... and I get acceptable performance. Most of the time "junker" PCs are easy to find free or almost free.
Hope this helps get you started on the road to insanity (along with the rst of us).

best,
....................john

Intel i7 960 quad 3.2G LGA 1366, Asus P6X58D Premium, 750W Corsair, 6 gig 1600 DDR3, Spinpoint 1TB 720