OK, I think I've got it!
All I've done is added the following parameters to the desktop shortcut (to imitate the 'Standard' shortcut the game defaults to), -reduceanimation -reduceflics -reduceimages -fpslock . So basically, no videos/cutscene animations run at all, so that fixed the success screen crash. And I've tested it on a few of the starting levels and I've not experienced any crashes, I've even tried to load up Baz's Mod which starts up ok (haven't completed the first level yet to see if it's crash-free.
ALso, I've managed to get the in-game music to play using the fix uploaded here: https://www.rockraidersunited.com/guides/lrr-music-without-cd-fix-r11/
So all swings and roundabouts from here hopefully haha, thank you all so much for your help, I really appreciate it.
One last question, is there anything that could be done to make the playing window a little bigger, I know that fullscreen doesn't work well at all, but it's difficult for me to concentrate on such a small window for up to hours on end, especially with Baz's mod. Any tips?
Thanks.
-Chin