I'll stick to your questions rather than toss around speculation about the owners of such rifles.
1. Why are most 223 and not a more powerful round like 30-06 or 308?
2. What accessories do most people think are must haves?
3. What is a quality scope for someone who has never used one?
4. What manufactures are best/reliable at an affordable price?
1) It's mostly the natural outgrowth of the AR-15 platform being popular. The M-16/M4 family of rifles uses 5.56mm, which is closely related (but not identical) to the .223 Remington. Hence, the predominance of .223/5.56 rifles. The round is plenty effective against two legged predators (there's more effective, but it works), relatively inexpensive, and has very little recoil. Depending on the platform you'll see other calibers come into play (for the AK, you'd be talking 7.62x39 or 5.45x39, the FAL and CETMEs are indeed .308).
2) Depends on your uses. For a HD gun, a close quarters optic and flashlight are common. KISS (Keep It Simple, Stupid) rifles also have a good following (no accessories beyond maybe a sling).
3) Depends on what kind of shooting you plan to do. For close quarters type optics, Aimpoint and EOTech rule the roost. For close to medium range, Trijicon has many followers. For long ranges with traditional magnification, there's no end of possible choices.
4) Hard to say; depends on what you find reasonable. For most folks, Bushmaster, Armalite, and Rock River are good choices. The extra hundred or two for a S&W M&P, Colt, or BCM can be worthwhile. If you're more into the Ruger Mini series, those are decent rifles.
However, I note you live in New Jersey. Your state laws are insane, so I'm not even sure if any of these options are available to you.