Pool is 45x20How big is the pool roughly? Theres mo need for 4 skimmers usually 2 is common a 3rd maybe on a huge pool.
For runoff get silt fence amd set it up the right way dug in with a pick or cover the bottom flap with dirt. If you got access to cheap haybales nearby they are best. If you can do flat work you can do this. Its fine to do small sections. Get some structural bonding epoxy and a hammer drill and pin it every foot max or equal to what was there. The old days 12x12 was common for everything on rebar grids. Chip and clean out anything that's loose or doeant look good. Make some primitive forms out of anything lying around amd paint brush on some binding agent before you pour it. I can't stress enough clean concrete. Like washed amd blown with a compressor or vacuumed dust is your enemy when bonding old amd new. An electric mixer is great for these jobs you can bang out 80 pounders fast. 5000 mix off the shelf is good for repairs and stronger than whats there. The skimmers are tricky but doable. Also dont fuss too much on transition from old to new being flush the plasterer will fudge variations so close is good enough in this application.