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I'm guessing your drain is not vented. by Rudy36
Which would explain the air gap. Just get a sink with the correct number of holes and get a pretty new air gap for it.
It's not a difficult project, the hardest part will be getting it out, usually.
You may want to consider just buying a new disposal at this time, however you should be able to buy a new disposal drain to install into the new sink that your old disposal will attach to. Removing the old drain could be quite the chore.
The disposal electrical will stay the same, however you might have to run a longer wire from the switch, which isn't hard, just attach new to old under the sink and pull through to the switch.
For water lines, buy new hoses that screw right onto your shutoffs and your faucet. So much easier.
The plumbing of the trap is probably your hardest job, as you'll be reducing from two to one, but it's not rocket science. Be patient, don't be afraid to buy too many cheap plastic parts initially, and don't overtighten. Water does not defy the laws of gravity.