I built a clone of my work M4A1s for training continuity when not able to access a work gun. I wanted it to be as close as possible to the issued item to ensure “plug and play” compatability. I made one mistake though- I had a PWS FSC556 permanently attached to bring the barrel length to 16"- the problem is that it is so effective as a comp I can get lazy behind the gun and not run it quite like I do with an A2 comp equipped M4.
Anyway, I put on a Knight’s RAS like the issued item. That’s pretty-much irrelevant to you since you are getting a quality rail system with the gun.
If you know what optic you will be issued, you will benefit from picking one up immediately to begin your personal quest toward excellence. It is also worth it to pick up an identical BUIS to whatever you are issued.
Get a good 2-point sling. My vote is for the Blue Force Gear VCAS. The VTAC is also nice, and there are other many other good options, however I personally prefer the VCAS over them all.
I also highly recommend getting a rail-mounted sling attachment of some flavor for the M4. I personally prefer low-profile types like the CQD forward sling mount. The placement of the QD on the Noveske is good, and if you want to keep QD caipability you can easily go with the Daniel Defense QD rail mounted sling mount for the issued gun in the same place.
Along with the front sling mount a rear attachment point at the rear of the receiver is way better than attaching it to the buttstock. Since replacing the end-plate is generally verboten the PR-4 is an excellent clamp-on adaptor that you can readily remove in case of idiocy that does not alter the base configuration of the weapon.
You need a light. Easiest answer is the VLTOR offset light mount with a SureFire G2. The VLTOR absolutely reeks of quality and the G2 is a proven, tough light that is easily replacable (everyone should deploy with at least 2 of these IMHO).
Don’t forget about other pieces that might be on your work gun (such as PEQ-2s or 15s) and account for them when planning your lay-out on your personal gun. It makes little sense to train with your light in a position that will conflict with your laser, only to realize it too late. FWIW- though my adaptation of and around the system I have found that having the laser module mounted a 3 oclock and the light at 1030ish works the best for me. If you are using a VFG and a full-hand grip (chicken-choker) you may find that 12 oclock for the laser and 5 oclock for the light will work best. Make your crap work for you, don’t let a first-impression mounting position dictate your use unless constrained for some reason.
Get some good lubricant for your gun. Carry a small bottle on your gear with a larger reservoir in your third-line. I am a recent convert to Weapons Shield- it’s good stuff. Avoid grease for operational use unless you spread it very thin and follow with liquid lube; then again, for the effort, you could just apply a decent liquid and be done with it.
Quality training is worth it, and price is relative. Cost is a mindset issue. Every dollar you spend with a quality instructor (Vickers, Rogers (both), Awerbuck and Gonzales spring to mind) will directly transfer to increased skill and knowledge. It’s your life, take accountability for your training. I have been in several open-enrollment courses that included active-duty guys that get some of the best training within the military. If they are attending these courses on their own dime you can bet the instruction is worth it (once agin I am speaking about top-level courses, not “Uncle Ned’s Advanced Bump-Firing Course”). Do not waste your money on a course that does not have an AAR from a knowledgable shooter. A low-light course should be at the top of your list. Dean Caputo’s operator class is awesome for learning how to keep a good gun running, easily giving you 5 years of direct experience in 2 days.
And of course magazines and more magazines.