#2: The 'HRW21 is a wider track than usual. The idea is that twist (moment) loads are handled by a single rail rather than a pair. To help with this, the track is wider than usual (better handling of twist or moment, that would otherwise be spread across 2 tracks). How heavy duty or not it is I don't know, I figure you use wide tracks where there isn't room for 2 tracks side by side.
I can't tell you if this is strong enough for your application, read the specs I guess.
Easiest cure for the CNC bug is to actually try and build something