As the OP on this thread I thought that some might like to hear the out come of my build.
I completed my Lower build with very little issue. The only problem I had was that the hammer was not turning freely. I deburred the pin hole that improve the situation only slightly. I ended up having to sand the hammer pin and the slots the spring ride in. The lower parts kit was sold to me as a rock river, but there was nothing in it identifying it as a rock river product.
I did fall for the BHO panic and paid more than I should have getting a completed Bushmaster upper with Carry handle and A2 style front sight. It included a no frills round hand guard and no rail attachment points.
As far as upgrades go that I was asking about. I went with no name low end versions. I found an AMBI safety, single point sling mount, and charging handle latch. All of them were less than $60USD extra. I am glad I did all three upgrades.
I am sticking with the rear sight in the charging handle. The main reason for that is that the flip up sights or aftermarket rear sights do not look as strong and sticking up that high I am afraid that the rear sight will take a bunch of abuse. I will get a flip up rear sight when and if I decide to go optics.
The Ambi-safety allows me to safety off with the thumb and then go safety on with the trigger finger with less breaking of my shooting grip than I do with just using the thumb. That could be overcome by training, but now I can safety on and off the same way with either hand.
The extended changing handle release, without an optic, is not a required change but it does make charging the rifle easier with the blade of the left hand. You do not need to come over the top. I do not have a lot of rounds down range and want to take a carbine class this year to confirm, but I believe that it will require less movement form firing position to activate in a failure drill. Less movement will equate to faster clearing and back on target.
Still to come:
I am considering a white light. That is going to mean a rail attachment pint some place. I have not completely made up my mind but I am thinking about a rail that mounts to the A frame of the front sight. Practicing with that will force my off hand up forward, where I think I want it, and should be accessible from either a Left index finger or a right thumb. The other option would be to replace the hand guard with something like a Magpol where I can attaché a short rail at the 2 o'clock position. I do not want a quad rail for what I do I do not see a reason for it. No coffee makers or fish bubblers here.