More than you wanted to know...
Congrats on the new purchase.
I've got a couple ARs myself and I'll try to clear up some of the confusion. I'm sure there are some knowledgeable folks here, but please check out m4carbine.com and ar15.com if you want more info on the platform, they have tons of knowledgeable members and info threads about the weapon. (I'm Krusty783 on both forums.)
I'll see if I can clear up some things:
First: Barrel features
From Bushmaster's website, it looks like your rifle has a lightweight or "pencil" barrel (.625 OD). Standard AR barrels are called medium or government profile (.750 OD). The term is not completely standardized, but Gov't profile barrels less than 20" have a channel machined down to around .625 in front of the sight post/gas block. This is for mounting an M203. This sight shows the profile of the different barrels:
AR15BARRELS.COM - Barrel Profiles
You don't need to think about changing your barrel for a gov't or hbar or heavy profile barrel unless you plan on doing lots of mag dumps or shooting long distances consistently. The accuracy difference between a LW and heavier barrel profile inside of 150-200 yards will be within the margin of error of your groupings.
A more important feature is the barrel twist rate. Your barrel's caliber and twist rate are stamped on it somewhere. The most common rates are 1/7, 1/8 and 1/9 (1 twist in 7", etc.). 5.56/.223 ammunition is a bit unstable, and heavier bullets require faster twist rates to stabilize. 1/7 is Gov't standard and is most common. I've only seen DPMS uppers consistently use 1/8 barrels, and I've seen very few 1/9's. A 1/9 twist should be good for bullets up to about 65-69 grains, and 1/7 is good for any bullets you can get your hands on. (There are also 1/12 and other twist rates, but your barrel is definitely 1/7, 1/8 or 1/9).
Second: Iron Sights
Front sight posts or gas blocks like yours with 2 bands are usually held in place by taper pins that go through the bands and into the barrel. It looks like Bushmaster just uses an A2 front sight base and cuts the top off, which is a cheap move if that's the case (judging by the pic on their website). For a few $ more they could have used a railed gas block or a flip up front sight.
You can replace that front sight with a YHM / Midwest Industries / GG&G / Someone's flip up sight, or get a railed gas block and put a flip up front sight on it. Or, you can buy an A2 Front sight if you wanted a fixed front sight post. You can install a railed gas block or flip up front sight without having to change your handguard. Here's the GG&G one:
Bolt-on Flip Up Front Sight - Clamp on Dovetail Sight Rail
Just Google "Replace AR-15 Front Sight" for videos on how to do this.
You can then get almost any fixed or flip up rear sight you want. Except the "Micro" sights because these are lower than standard sights and are meant to be paired with each other. Magpul MBUS sights are the cheapest you'll find at about $50-60 for the rear.
Third: Reliability
Aside from matching the buffer & spring to the gas port, the main reliability point of pain of an AR15 is the Bolt Carrier Group (BCG). The Official Mil Spec for the bolt calls for several quality control and manufacturing features to ensure the bolt is designed and assembled correctly.
These are:
Magnetic Particle Inspection (MPI) Which checks for small cracks.
Shot Peened (Stress Relief)
Pressure Tested/Test Fired
Staked Gas Key
It's not clear which, if any, of these processes have been followed in the manufacture of the Bushmaster BCGs. Since you're only taking your rifle to the range (and not your cruiser/the sandbox), keep it stock and shoot it. Then shoot it some more. When you get some money and the market slows down a little, but a new BCG which has been MPI inspected and test fired, etc. and sell yours on Ebay/Gunbroker/Armslist.
New BCGs run about $230. You can also find BCGs which have a Nickel Boron (NiB) coating which is supposed to make them easier to clean, and silver. You can buy a NiB carrier if you want, but that's up to you.
Finally, ARs tend to like running wet especially for the first few hundred rounds while everything wears in. It's a good idea to get some quality lube and strip, clean, and lube your rifle before you go to the range and take some lube with you to the range. For an AR, "quality" lube is anything more viscous than remington oil. SLP-2000 and Frog Lube are 2 of the "premium" lubes out there. You can use either one of them, CLP lube, or even Mobil 1 5w-30. Seriously, there are quite a few professional AR operators who use Mobil 1 synthetic 5w-30 in their rifles. Google how to clean and lube an AR-15 and you'll find all the help you need.
I hope this helps. There is several metric tons of info about ARs on the interwebs. Google is your friend and can probably answer any question you have about the rifle. If not, email me and I'll try to help.