It really depends on the software and hardware that you wish to add to the basic machine. There are many graphics cards which will work well with System 7.1.x or 7.5.x, perhaps not 7.6.x. Ditto for image grabbers, graphics accelerators etc. 7.6.1 is usually more stable, but it might be worthwhile buying a hard disk to swap in and out. Personally, I'd start out trying to run System 7.1.
Formac products were distributed in most European countries from the start of the company. I used a Formac monitor for many years and encountered many expansion cards in 68K Macs at work. It is likely that your PDS card was reviewed in at least one of the European Mac magazines in the early 1990s. Early Formac products (basic graphics cards, LC family accelerators) appear to have been designed in house, alongside rebadged/reworked CRT displays. More advanced products (3dfx graphics cards, LCD displays, G3 accelerators) were developed with partners with Formac input.
Have you had a look at Waybackmachine to see if any Formac pages have been archived?
Have you used a system utility to see how your Mac is described? A PDS accelerator often works without any drivers.