Yeah, I should have been stronger on the light. My living arrangement makes a light not as vital. It's never really that dark where I stay and there is a very low likelihood of a friendly being mistaken for a bad guy. For most people a light is essential. I have one on my AR and also on my M&P 45 2.0 just in case. I don't have one on my carry gun. (M&P 9 2.0 compact)
Also, good call on the sling. Just have to make sure you drill for it. You don't want to be fumbling around trying to get the gun on right if God forbid, you end up needing it quickly.
There a few different sling configurations and several companies making good slings and mounts. Not as many as with other parts though.
IMHO can't go wrong with Magpul. Especially for mounting accessories though their slings are excellent too. I would stay away from the bargain stuff on Ebay and Amazon. (don't ask me how I know)
I think the OP mentioned somewhere along this thread that he also is not rolling in money as is my situation as well.
It takes some skillful and sometimes patient research and shopping to get the best bang for your buck.