I'm sure some of these points have been covered somewhere in the last two pages of posts...so bear with me if I repeat any of them.
As you can well guess...M4's are the "Honda Civic" of the AEG world. There's a mind boggling array of upgrades/options/just-plain-silly-things to swap/attach/etc...to your M4.
Some guys are really particular about replicating a certain authentic look (i.e. they'll look at a photograph of a Navy SEAL and aim to setup their rifle just like that)...others go down the more practical route (i.e. if your mount isn't the specific Wilcox mount, or ARMS #20 base...that's ok, as long as you can shoot straight with it).
If you're starting off with a "stock" appearing M4...one of the most important things to sort out first is the battery. What size, what shape, where are you going to put it. It'll affect a lot of configuration options.
Aside from in the front handguard...the two most popular options are to stick it in a PEQ box (mounted left/right/on-top of the RIS)...or in the stock (Crane, MOD, Clubfoot, etc...)
Taking off the front sight and all that jaz isn't too hard...take your time, use the right tools, go easy. Or take it to someone who'll show you what's what. If you have someone do it for you, it'll take them about two hours to swap them out and ensure everything's working nicely.
There's so many different rails and setups that it's pretty tough to recommend one particular setup. Having said that, I've had great success with free-floating handguards/RAS setups that I've partial to them (i.e. Noveske, Daniel Defence, JP Rifles, VLTOR CASV, etc....). No matter how much torque/stress you put on the handguard, your barrel doesn't get pulled out of line.
I also prefer either a plain gas block (and mount flip up sights on the top rail)...or flip up front sights that are integrated with the gas block (i.e. VLTOR, ARMS, etc...). If you're running exclusively optics (i.e. RDS, magnified, etc..) you can usually skip iron sights. Where I've had both a red dot sight and flip up iron sights....I've only used the flip up sights once, and that was when I forgot to change the batteries (which is the point of having both I suppose
....but if you remember to change your batteries, then it's hardly ever an issue).
My last three M4's barely had any rails on the handguard. Aside from a vert grip I didn't bolt anything onto them. Handguards that are "modular" (where bits of rails can be bolted on or off for a clean look) are nice that way. Some examples are CASV, JP Rifles, Gemtech TALON. My latest M4 has a lot of rails on it...but I just haven't decided on the setup...I'll take the unused rails off when I sort that out.
If you end up with a standard Aimpoint...you will need a mount to attach it to the top rail. A high mount gives you a bit more comfort with a more heads up positioning. A low mount can be tough to see through with big paintball goggles (as especially with a paintball mask). A high mount isn't too bad (still awkward though) will a PB mask.
Best of luck...don't be shell shocked by Huangs place! LOL Call ahead to make sure he'll be there.
PS. If you're nice...ask him to setup a handguard with all the bits in place...then you'll see what's blocking (or not) what.