Going to start gathering the parts for my first AR build.  I want to build a CMP-legal match rifle, so my requirements are a bit regualted....

This is what I have in mind...

MEGA lower receiver (if I can ever get a hold of the guy).
RRA lower parts kit
RRA National Match Trigger
Standard A2 rear stock and grip
White Oak Armament 20" stainless CMP Rifle Upper with pinned rear sights

Question...

Bolt Carrier Group... I guess I can go with a CMT M16 BCG - MP Tested   Anyone see any issues with that? I thought about spending the extra money on a Less Baer National Match group, but I guess their's no real benefit to the accuracy and precision of the rifle.

And I guess I need a sling and standard charging handle.

What else am I missing?  Besides good ammo and assembly tools?

Oh... and a bunch of magazines.

Quoted: MEGA lower receiver (if I can ever get a hold of the guy).

Is that the one with the "Gator Grip"?  If so, don't bother.  The "Grip" may have cool factor but it violates CMP rule 6.1.3(6).  If I was you I'd pick up a complete RRA NM lower and be done with it.

White Oak Armament 20" stainless CMP Rifle Upper with pinned rear sights Question... Bolt Carrier Group... I guess I can go with a CMT M16 BCG - MP Tested   Anyone see any issues with that?

The WOA upper is fine as is and includes the carrier and charging handle.  A Les Baer carrier offers no competitive advantage and lightens your wallet for cash you'll likely need for other equipment or ammo if you're just starting out.

You may want to think about the aperture and front sight width before you order.  If you're young ( 20s ) then a .036-.042 rear and .052 front will probably be fine.  If you're mid 30s or older then I'd go with a .046 rear and .062 front -- but these parts are fairly cheap and easily replaced so you can get a couple apertures and an extra post and mix and match 'til you get what works best for you.

And I guess I need a sling and standard charging handle. What else am I missing?  Besides good ammo and assembly tools?

For a sling I'd look at a leather 1907 sling from Turner Saddlery or Les Tam.  The Turner synthetics take some getting use to but have their advantages.  As for ammo, depends on the matches you're shooting.  If you're shooting 100yd reduced I'd stick with the 52/53gr match, for across-the-course go with 75/77gr and 80 SMKs for the 600yd line if you reload.

Mags?  Stick with GI 20s and you really only need 3 or 4.

HTH and welcome to competitive High Power...