Well bro, it's about personal preference.
The YHM fore end that I linked was one of a couple of styles they have, and one style has a rail on the top and one on the bottom for mounting a pistol grip front end if you wish.
A CMMG lower is fine also. There really isn't much overall difference and some companies buy theirs direct from CMMG and have them stamped with their own name/image on there.
Unless you are buying one from a CNC shop that is personally cutting the thing for your build, most receivers are exactly that. Mass produced and marketed receivers....
As for the CAA mount. I have seen them. I am not a huge fan of them, because your glass is going to cost you good money, why skimp on the mount that is going to hold it to the weapon? Kind of doesn't make sense to me, but that's just me.
What I don't like about that particular mount is that there is only one screw that holds the whole thing down, so there is only one point of contact to the weapon, yet it is supposed to align both ends of the scope in line with the bore and keep them there. Not the best application of theory in my book, but plenty of guys seem to like them. For a CQB style weapon, I am sure it would be fine. For a long range varminter, probably not.....
Both the scopes you reference are fine. Nothing wrong with either one. IOR Valdada is making great scopes and Millet has been around for quite awhile doing the same thing. Both would be fine for your standard 16" barrel profile weapons.
( NOT DJ )