Welcome and good luck on your reloading decision. I reloaded for about 30 yrs, don't shoot much more than you, but enjoy the "process" and the fact that it costs less per round (after you recoup the initial cost, of course).
I can't be much help. Nowhere have I read that it was designed to mimic the characteristics of AC. Rather, it's promoted as being a lower flash/cleaner version of Reloader 15 and is supposed to run best with heavier bullets. Run a google search and you'll probably find many more opinions. FWIW, I've started using AR-Comp early this year when I was running out of 223 powders and it was available. I've been satisfied with it; it meters nicely and produced nice groups with loads from the upper and lower ends of the load spectrum using 55 gr Hornady. I'm getting ready to work on some 69 gr. SMK loads.
See above. Is that an indented ring or can it be cleaned off. Also, bullet seating depth looks a little shallow, you might benefit by seating to the middle of the cannelure.
The questions are a bit open-ended. See the comments re: reading manuals and whatever else you can get your hands on. You'll find the reloading process slower than running pistol rounds through your press. Not only do you need to be concerned about case trimming and case lubing (unless you already lube pistol cases) but If you scrounge brass you'll need to swage primer pockets. I've been happy with Lee and Hornady dies, but I'm sure other offerings would be as good or better. Also, read up on rifling twist rates and bullet weights.
There was an article in "Handguns" several years ago called "Make it Right with a 40 Lite" that discussed a number of reduced loads for the 40 SW. You should be able to run an internet search on it to find an online copy. It is an interesting read.
In as few words as possible, find and use load data for 185 gr lead and the powder of your choice (I'd probably chose 7625). You can run a search on this BE subforum or go to the powder mfg's load data on the web. One of my manuals has a start for 7625 using 185 lead as about 5.5 gr.; but don't take my word for it or anyone else's on the internet. Do your homework and you'll find solid data from bullet or powder manufacturers.