We managed to get a sink, disposal, drain, icemaker, and outlet in our 65" X 30" island, and still have three drawers and some undercounter space. Here is the island while I was building it (with no top). The section furthest away from the camera is for the icemaker. To the left is the space for the rectangular sink. To the right, you can see the three drawers. Here it is completed: The drain goes through the floor, and serves both the sink and the icemaker. There is also a small vent under the sink.

My experience as a non-pro, most of the the chrome-plated brass pipes (bathroom & kitchen) used in my Chicago condo corroded and leaked within 10 years of installation, and now all the chrome/brass pipes in my home kitchen are in various states of corroding. The cp brass wall tube from my disposal just crumbled when I bumped it during an RO filter servicing, and ripped apart when trying to separate it from the J-trap. I have not had any issues with the PVC replacements, and they a third to a fifth of the price of a comparable chrome plated brass piece at Home Depot. Seems like replacement with PVC/ABS is a no-brainer if it's not visible and not a code violation.

Just slap some pipes together! (Just kidding - don't do that!) Based on your "new DIY" posting, I'd strongly suggest getting some help to learn. Even hooking up a plain old sink for a rookie can be a challenge - this is tricky in several respects for a novice. (too many places to have leaks, for one thing).

Cannot speak to the code that might or might not apply in that jurisdiction. Check valves not required in my area. The check valves in the supply are not a bad idea. They prevent water from the sink or faucet being drawn back into the supply piping if the supply piping should experience a negative pressure. An episode of the TV series Quincy, M.E. with Jack Klugman featured this problem. The problem is called "cross contamination". I think the episode is Season 5, episode 21 "Deadly Arena". Suppose that the restaurant is located on a hill. Someone hooks a hose to the spout on the faucet to wash vegetables in the sink. Some dirty water is standing in the sink. The open hose end is in that standing water. A large fire breaks out nearby at a lower elevation. The hydrants are used such that the water pressure up the hill at the restaurant becomes lower than atmospheric ( vacuum). Dirty water could be drawn into the supply system from the sink. Plumbing is two distinct systems which are NEVER interconnected. One is SUPPLY, the other is DWV. Faucet spouts (by code) never extend down below the flood rim level of sinks and tubs so that an air gap always exists between the two to prevent cross contamination. It is reported that a prominent physician said that modern plumbing has done more to improve the health of the American people than has all of medical science.