I should be receiving my new 6.5 Grendel upper tomorrow. Strictly out of convenience and buy it right now availability it is a standard CAR upper, flat top with an A2 front sight post.

I'm thinking of picking up a LaRue/Troy folding rear sight. Will this be on the same plane as the A2 front post or do I need to look at a different sight?

My eventual plans are to go with a LaRue 10 or 11" quad rail and low profile gas block but I don't have the extra cash for that right now. At that time I plan to pick up the folding front sight to match the rear. When I do that will my front/rear sight be on the same plane if I mount the front flip up on the rail? Mu current setup has my front flip up mounted on the gas block which sits lower than the rail.

Also, by mounting the front sight on the rail will I need to put a riser on the Eotech so it won't be in the line of sight when folded?

Pretty much all rear sights are compatible with all front sights, as long as you understand the gas block vs rail mounted front sight height differences, so no worries there.

Most will clear the Eotech pretty well when folded.  The main reason for the riser is to co-witness the BUIS in the lower 1/3 of the Eotech window when the BUIS is flipped up, vs absolute co-witness in the center of the window without the riser.  It's only an extra 1/3", so aside from co-witness, there's not a lot of difference.