It would help if we kind of knew your overall vision for the gun. Like if you did an image search for a carbine that strikes your fancy, how you would like it to be set up, I'm sure people could give you a range if options from inexpensive(not cheap in quality) to mid range. One thing I would definitely do is set aside a few bucks for a decent trigger (ALG QMS $50ish, LaRue MBT $100ish or Geissele G2S $120ish) would be my picks for a trigger.
The next important thing you'll want is a better charging handle (Strike makes one that's decent $25ish, BCM Gunfighter $50ish-$80ish(ambi) and probably the most popular The Radian $80ish and Geissele Charging Handle is also nice, $100ish. Of course all these items ebb and flow, sometimes if you hunt or wait for just about any holiday you can save 15%-20% or get free shipping.
Lastly, a good sling, like a Magpul or a Blue Force Gear or a Trex Arms are all good quality. I have some sub $50 slings I've used in the past and they are holding up well but the ones mentioned above are what the cool kids and pros are using.
I can more than make due with a standard Mil spec T6 stock like you have but if you want something a lil more refined the BCM, B5systems or just a good ole Magpul (many models) are all popular.
Take a look at AR/M4 setups in Google images and you can post and get lots of good input from people here. I splurge in some places and am thrifty in others. But a good feeling trigger is important (to me) and so is a 7075 grade aluminum Charging handle is too, mostly BCM's, started with em and just like em but I like the Strike and Radian just as well. The BCG you got is probably from a mil spec supplier and is probably ToolCraft and totally fine, but having a Sprinco extractor spring and sprinco buffer spring is a worthwhile upgrade imo, but those are pretty cheap upgrades that do nothing aesthetic wise but the Sprinco spring for your buffer spring in the appropriate configuration according to your gas system (mid length or carbine) will take that annoying twang and secondary pulse you get when you fire a shot and I absolutely hate that twang so it would be a must have for me.
Sorry, it seems like a ton of information but really it's just a few hundred bucks worth of stuff you can easily order and easily install over time to refine your carbine to your preferences and help it shoot a lil better and perhaps a lil more reliability. I am biased toward PSA because I've done a couple of their kits and been really pleased, along with their business model and commitment to customer service, etc.... nice carbine.