/vr/ - Retro Games

Don't know where to post it but here it goes.

For a while I've been planning on making a Quake-like (but as a really amateurish game-dev who's only been modding Quake I'll be settling on making a top-down shooter with Doom's structure) with the same aesthetics of late 90's shooters (mostly Unreal/UT).
I figured using something close to the Quake1 engine would be the best deal because the player physics and movements are simply the best in the whole series, but just using the original idTech2 engine would be too limiting compared to what late 90's shooters were capable of.
I looked at the Darkplaces engine but it changes the player physics to the one in Quake3s, and changing the protocol back to Q1 adds too much complications.
So then there's Half Life's engine, which is essentially idTech2+. It seems to be the perfect candidate (and considering Deathmatch Classic as seen in >>3237716), but the texture filtering is so damn ugly compared to Quakespasm's and I don't think Valve allows people to make commercial games for GoldSRC.
But then I came across some sort of open-source version of GoldSRC: http://www.moddb.com/engines/xash3d-engine
Does that mean I can make a commercial game out of this, or will that bring me lots of legal trouble?