Replacing My Kitchen Sink – Should I Add an Air Gap for the Dishwasher?

Hi everyone! I'm planning to replace my really old dual bowl kitchen sink (it's been around for about 30 years) with a new single bowl. Since I'll be working under the sink, I was wondering if I should also add a dishwasher air gap while I'm at it? I eventually want to replace my dishwasher too. I know my state, Georgia, now requires it, even if my house didn't when it was built. I've read that the air gap needs to be mounted through the countertop, but can it be placed underneath? Also, I've noticed a vent on one of the taller pipes connecting to both the main sink drain and the dishwasher hose—could that be the air gap? I heard having the hose elevated can work but might not be code compliant. Here are some photos of my current plumbing setup: [photos](https://imgur.com/a/f7yMh72). Thanks for any advice!