I ordered the "Colt LE6920 OEM2" that has no sights/no furniture.
My plan was is to go with Magpul stuff, but wanted to check the collective wisdom to see what other stuff I should look at...
Thanks in advance for suggestions.

The Centurion C4 rails are amazing. Same can be said for the Forward Control Design RHF4 rails.

The OEM2 lacks the delta assembly and front cap, so you can't just stick a Magpul hand guard on it. You'll need to either go with a free float that clamps to the standard barrel nut (like Tig recommended) or switch it out for one that uses its own barrel nut.
For the buttstock, I'm a fan of the simple Magpul MOE carbine stock. You can usually pick one up on the EE for around $25. And I'm one of the few that still uses the standard A2 pistol grip, but Magpul makes plenty of good grips. The standard Magpul BUIS will work just fine as well.
When you install the trigger guard, please make sure you support the receiver when installing the roll pin.

I'm damn partial to USGI A2 grips and type II waffle stocks.

I vote Centurion rail. I've acquired a few, they will spoil you.
add: and Colt has some of their rails on their builds.

For a cheaper option to the Centurion, Midwest Industries makes an extended carbine 2 piece free float rail as well. I have the midlength extended and it is nice. Got it with a nice LEO discount.

You're going to have to look for something that clamps around a standard barrel nut.  Else, you will have to remove the pins for the gas block.

My only AR with a free float rail on a std barrel nut has a fortis rev2. I like it and it mounts up solid.