3. There are replica ACOG sights that have a little Docter Red Dot sight on top. That would fit your need of having an RDS as well as some magnification. Even the 4X magnification on the ACOG is overkill though. Our guns seldom shoot that far accurately. Its more likely that the BB will lose velocity or be blown off course. You'll be able to see stuff but not hit it
4. I use a 'gripod' as they say. Its basically a vertical grip with a spring loaded bipod built in. Works well so far.
Not the one i have...but basically like that
6. The magazines with the feed door and winding wheel are high-capacity (hicap) magazines. They usually hold 200-500 BBs and you can have a constant stream of BBs flying out by periodically winding the wheel to keep tension on the spring. Those ones you add BBs by pouring them in through the feed door.
The one you have is more likely a midcap (mid/medium capacity?) or locap (low capacity). Midcaps hold 60-120 BBs and locaps usually have 20-50 (you will also see 'realcaps' mentioned which are basically real capacity ie. 30 round magazines)
You need a loader to load lo/midcaps since you push in BBs and compress the spring, and a little latch at the top keeps the BBs inside. Plunger loaders are slow, there are the pistol mag loaders which are like a BB-injection, just insert the tip on a lo/midcap feedhole and keep pushing the injector with your thumb.
As said, dont use loaders on hicaps.