What type of electrical boxes should I use for outdoor fixtures when fiber cement trim openings are narrow & shallow?

I haven’t heard from the electrician who wired my house for 5 days and prior to that was just a short text to say our contract didn’t include installing light fixtures for a remodel. I live in a rural area, so contractors are hard to come by. I can do basic wiring.

My questions concerns electrical boxes for PPG fiber cement light blocks and outlet blocks. The blocks are trim pieces for outdoor electrical fixtures. They have very narrow and shallow openings.

The light block is 1.25” thick x 7.25 wide x 9.5 high. One block has 2 cables protruding and the other has 1. A 4” diameter pancake box was slightly too large in diameter.

My light fixtures are Bellagio 16.5" high, bronze downbridge outdoor wall lights. The backplate is 6.75" high x 4.75" wide. They weigh 4lbs.

Question: What type of light box should I use to enclose my wiring? Should I use a metal 3.5” octagon box 1.5” deep? I want the light fixture to sit flush with the trim.

The outlet block is 1.25” thick x 5.5 wide x 7.5 high. I tried a 1 gang, 1” deep blue PVC flanged shallow box, but it was too wide. I found a metal box that will fit, but it is 1.5” deep. I was hoping the face of the GFCI outlet would be flush with the trim. The outlets will be protected by waterproof boxes.

Question: What type of outlet box should I use? Should I stay away from metal? Also, one outlet block has 3 cables protruding from it.

Question: The final question concerns how the cables protrude from the sheathing. In several cases they’re not in the center of the opening. Should I use a jig saw to cut into the sheathing to reposition the cable to be able to pass through center knockouts?

Thanks!