It's not just impressive, it's mighty damn impressive.
There are some sites with great tutorials and guides. Firstly TWHL, then GameBanana (I've written some there) and ModDB. There's also Valve Developer Union and Sven Manor (which is more SC-specific, but I've seen GoldSrc-universal guides there).
I think you can also find older ones in TWHL's links section. (not sure if it got removed switching from TWHL3 to TWHL4)
If real-time help is needed, there are the Shoutbox and the TWHL Discord.