I was given a Nikon Coolpix 900 (1998 model) but there was no CompactFlash memory card. Basically in so many words the original package came with a: EC-8CF 8MB CompactFlash card but now I am questioning whether or not I need that exact model (likely an eBay purchase at this point) or can I get a different model with similar size? For context it becomes harder to work with above 200 Mb.
Even though there are several variations of CF cards (multiple versions of CF which are backward and forward compatible, IDE, CFast) the camera definitely expects generic Compact Flash. You are definitely not going to have any issues with different brand of cards and different sizes.
The only reason there was a 8MB card in the package is for test purposes or basic usage. Almost all cameras had a small card in the package. 8MB is small even by 1998 standards.