1st off,
welcome to the site!
second, read around, esp the tacked threads and use your "search" feature--lots of these questions have been asked/answed and have many topics w/ many opinions....
1: imo, "No"--not for most uses; C-L is longer lasting (rnd wise), more corrosion resistant, easier to clean, and more durable for hard use, but the C-M is usually cheaper and will be a tad more accurate
2: depends on what you are looking to do w/ your AR and your budget...choose the optics that fit your needs--i'd recommend EoTech or Aimpoint for CQB and/or a nice one piece (larue, armalite, RRA) mount w/ a quality optic (SWFA Super sniper, Leupold, nikon, etc)
3: again, it depends on your budet and uses; i'd recommend YHM, MI, DD, KAC, Troy, etc overall....
FF/HG FAQ4: i prefer 1-7 b/c i tend to shoot both heavier and avg 5.56 loads; h/w, 1-9 is great for most commecial loads
read this:
www.ammo-oracle.com5: are you refering to the bbl style? if so, they probably mean a C-L lightweight profile bbl...
note: CM is the bbl matieral; h/w, a C-L is used to line C-M bbls
like i said, use your search feature and read around, good luck!