1. Can any company's barrel/upper reciever assembly be combined with another companie's lower reciever assembly?
There are some Colt iterations that have smaller pivot pins/holes, outside of that, you're generally good to go with any of the big name manufacturers.
2. Is putting the barrel assembly and the upper and lower receivers(both purchased fully assembled) together an easy task for a noob such as myself? Is this a good way to save money over buying a fully assembled rifle? What kind of savings would one get in doing things this way?
As stated before, not much to it. 1 take down pin and one pivot pin. Where your savings come in is purchasing a completed upper and stripped lower/parts kit. Not much too it if you are even a little mechanically inclined and take your time. Plenty of how-to's on the net -
www.ar15.com is a great source for the how-to stuff.
3. Can I be assured of a quality product if I choose amongst the following companies; Stag, Superior Arms, DPMS, Del-ton RRA? Any others i should look out for?
Out of those, not much to worry about. I personally would recommend both Stag and RRA.. those two I have experience with and no issue thousands of rounds later. Others to consider are LMT, Bushmaster and Colt.
4. Can the individual components (handguard, trigger, handle etc) be modified/upgraded at a later date easily?
Yes and this is where the addiction really kicks in... think of the AR platform kind of like you would a 1911 or even a volkswagon bug.. the sky is just about the limit. Remember that you get what you pay for as so many new AR owners find out the hard way.
5. Is a chrome lined barrel worth the extra money? I've got a $850 preliminary budget.
Can be, but as said before, Chrome-Molly will be fine.
6. What's the average distance limit a 16" barreled rifle can maintain "combat" accuracy (assuming the shooter is doing his part).
300+ meters for "combat" accuracy with a 16" barrel. Again that's considering that the operator is doing their part.