I'm just now looking to get a computer to play these old (and maybe new) Star Wars games. I'm just wondering if anyone knows why Shadows of the Empire hasn't been updated and released anywhere? I've got the first Dark Forces (on disc, actually) and that is older. I've read the book and comics and always wanted to try Shadows of the Empire.

Also...as a newbie who has only just gotten into this, can anyone tells me if I get a new PC with Windows 10, am I likely to have issues with the games? My old clunker currently won't play much due to the graphics card, but I'm not sure how the newer OS version will affect the older games I'm after?

Well, it hasn't been released, yet. GOG only started its deal with Disney/Lucasarts last year and since then, they've been releasing games from that catalogue in batches of about 3-6 titles every few months.
Unless there are severe compatibility issues with Shadows of the Empire, it's almost guaranteed that it'll come here eventually.

As for the other issue, nobody can say for sure if all games will run equally well on Windows 10, but reports so far seem to be pretty positive on that front. Once the system is actually released, GOG will introduce support for it, and probably try its best to make as many games compatible with it as possible.
At the very least, any DOS games should work fine, since they're running in Dosbox.

Why not Zoidberg?