Yes, after the clip is removed the piston assembly will slide out as 1 piece. Be careful not to let the inner mechanism unscrew from the piston otherwise you'll have a mess of balls and springs to deal with.
I'm not sure about the cross compatibility between civic rear calipers, but according to hondas parts catalog, the dust boot kit fits all trims from 2016 onward.
As for the replacement of the boot, I think you'll have to remove the piston, which isnt too bad as long as you're willing to bleed...
The parking brake doesnt automatically engage unless you're in the car with it in drive using brake hold then unlatch your seatbelt, then it will apply the parking brake.
I accidentally disassembled the piston when I took the caliper apart for the first time. I dropped one of my springs and I was never able to find it, so I had to do it with one less spring. I believe I did it with about 51 ball bearings and 17 springs, so I put in 3 balls and then a spring and...
Yes, use a caliper windback tool to completely screw in the piston. Then once you remove the motor and C clip from the rear of the caliper the piston assembly will slide out. Be sure not to let the piston assembly come apart after you remove it, or else you'll have a big problem.
I mounted mine under the passenger seat so I didnt take up trunk space. Theres not any audible vibration noise but if you sat in the passenger seat you would definitely feel it