"But won't that slight 1/8" reveal ledge be a crumb catcher and won't debris get caught in that 1/8" reveal ledge and under the countertop?"

No. I've probably installed a thousand sinks this way and have never gotten that callback.

1/8".

"Can a slight postive reveal as you recommend be as small as 1/16th?"

Yes.

"What would you say this positive reveal is?"

Looks to be about 1/8" to me.

Go with a strong 1/8" please. You'll never see the bulge.

Your cabinet person is wrong. That 36" Elkay is undermounted in a 36" cabinet and looks much better than if it were in a 39" cabinet. Throw away the leaky clips supplied by Elkay and install it with two Sink Straps please.

Yes, the tops of the cabinets sides are cut down about an inch, however, the strapped sink makes that irrelevant structurally.

" I also get tired of the guck that builds up where the granite meets the sink. it's not always easy to clean, especially if the sink is square."

If you have gunk at an undermount sink, that sink is leaking. Strap your undermount sinks and fabricate with a slight positive reveal and it's impossible to get gunk.

"Current front sink countertop is 5.25 inches (too much) but given cabinet construction fabricators think can only reduce to 4.5 inches. (we have 1.625 inch overhang already)"

Your fabricators are mistaken. Your front rail can be as small as 2 3/8" as long as your sink is strapped, not clipped or blocked, in place . Here's proof on a retrofit:

"Can we cut into cabinet cleat or rail to allow sink to come forward?"

No need; simply rabbet the top of the cabinet sink rail 1/8" to accommodate the thickness of the sink flange.

I'd follow Ruvati's 1/4" positive reveal recommendations, however, please disregard their mounting clip detail. Clips leak and drilling into engineered stone will void the warranty. Use a couple Sink Straps or a Hercules Universal Sink Harness please.

Flush reveals create an elongated silicone joint that frays and becomes contaminated, unsanitary, and ugly. The positive reveal exposes the least amount of silicone, looks best, and is easily cleaned. Ruvati specifically does not recommend a negative reveal.

https://www.ruvati.com/wp-content/uploads/C_Undermount_Workstation-1.pdf

" I need one for air-gap, one for water filter. How far to the left and right would you place these away from the kitchen sink faucet in the center?"

I'd go 8" on center from the faucet for easy cleaning. After inspection, abandon the goofy air gap please. A high loop in the dishwasher drain line seems to work perfectly in 45 states. I'd install a disposal switch or a soap dispenser in the hole.

j Brule:

While silicone does have adhesive properties, it is not the same as some of the structural adhesives like Black Mamba and requires the use of mechanical fasteners. I recommend a strap system like the Hercules Universal Sink Harness or a Sink Strap or two. Both can be retrofitted.

Diana:

Steel-on-the-flat is woefully inadequate for what you’re proposing; I don’t like it under any circumstances because I’ve fixed it a thousand times.

Square tube custom steel frame from the backs of your cabinet fronts, let into and across the wall, then to the legs and apron. No additional cabinet reinforcements are necessary.

"I gave the installer the Hercules Universal Sink Harness Kit but he said the plywood pieces he added provide good support for the sink."

Unlike a HUSH, the plywood pieces cannot push the sink against the bottom of the stone. Mounted this way, with the steel-on-the-flat divider, the sink will sag and leak. It is impossible to make a divided sink flex with a HUSH without violating the laws of physics.

"Is this the correct way to install an undermount sink?"

No.

"If the sink needs to be replaced one day, how can it be done?"

It would be done by popping off the cabinet front and prying off the plywood; a real PIA. Were it strapped with a HUSH, it would be a 20 minute job.

Remove the plywood. Place the sink in the cabinet with the HUSH. Install the top, then have your plumber mount the sink with the HUSH please.

This is what happens in two years if you get this wrong:

Jeanette:

As long as you have 3/8" or so between the sink top and the stone bottom, your reveal will be fine.

Please place a straightedge against the warped door and post a picture.