I played through the original campaign just fine, for the most part. I got these crashes sometimes when loading between areas (it's why you always save). Restarting the game usually meant I was good for a few hours. However with the Dragon Storm expansion, I have no such luck. I can play the first two missions just fine but loading into Sevenkeeps causes me to crash every single time.

I've been running the game's exe in compatibility mode already. The only fix I've found was to the game's legacy exe to play the old Gold version of the game but that seems to be Steam-only. I'm not all too keen to install 3rd party patches either. If there's a way to use the legacy edition then maybe I'll use it as a last option but until then, can anyone help me with this?

Thanks.

Try backup saves and remove entire game folder from users My Documents. Reconfigure it. Start a new game and if it work - restore saves.
If you use GOG Galaxy - verify game files, at least twice.

No .\Program Files (x86)\ , right?

Nope, I kept it the default directory for gog which is [Drive]:\Games. I'll give this method a try.