Digimon World 2003 is the PAL version and has a bunch of bugfixes and other stuff. Does it go in its own category on this game or should one attempt to get it added as a separate game?

I think it would count as an own category. The big difference is probably that Counter Crest is not working every time. However good luck to get that one added, nobody ran the PAL version yet. This should not stop you from running it, but don't be disappointed if it does not get added as a category. I can imagine that it won't. As a seperate game it wouldn't make sense probably. Even though there are quite a few differences, it's still the same game.

Yeah trying to get involved in older stuff like this when you live in a PAL region is a pain if you don't want to straight-up emulate the NTSC version.

you can get a used ntsc ps2 and an ntsc game copy "relatively" cheap on the internet if you really want to. just be prepared to pay twice as much due to the shipping fees... emulating the NTSC version is free. you should probably stick to that option if you're just starting out. slower loading times won't instantly kill your run. if you really want to go for a top time you can still switch to console when you feel like spending money.