The size of the sink base, you, select can hamper the installation. It's your choice.

Believe me, there are NO plumbing issues involved. What MAY be an issue is finding a hardware store--or other source--for the parts you need to do a changeover. The best thing you can do for yourself is get down and climb under your present sink, the neighbor's sink, your family member's sinks, and familiarize yourself with the plumbing that's under there !! While you're down there, check for leaks, and use a ruler/tape measure to get an idea of sizes. Bathroom sinks are usually 1 1/4" diameter thinwall pipe; the tub/shower and the kitchen sink are, or should be, 1 1/2". One thing to remember: the 1 1/2" thinwall pipe hooked directly to the bottom of your sink, and tied into the "S" or "P" traps under there, is NOT NOT NOT the same as the 1 1/2" drain piping; HOWEVER--there are adapters to mate the thinwall to the heavier piping. By the way, you ARE gonna go to the store and find out what a "P" or "S" trap is, aincha?? Dont be afraid to ask Q's, and do realize many of the guys you ask are about as ignorant as you are when it comes to plumbing....many--not all of 'em. THEN: when you find somebody who sounds like (s)he can help you do this project, and they put down on paper the parts you need, the best thing you can do is repeat the process--go find somebody else at another store who can do likewise, and then compare the parts recommended, &c. Maybe this soundz like plumbing 101--you're right, it is. Anything else spellz disaster in the making, not to mention the resultant feeling you bin ripped off and jerked around, and that you coulda done a better job yourself.... if only.... you'd taken to heart the suggestion of: kenn 1RmSchlHse millersport oHIo -- there's a time and place for spontaneity....

Sometimes a drip edge is installed below a farm sink and looks good as well as being practical. That would work for your half inch below the sink, the sides could be filled in with an overlay panel like Food shows. Google for images. Most farm sinks without an overlay panel look fine but your sink is significantly less wide than your cabinet, that is why it is more noticeable.

I had wantd a postive reveal on mine, for cleaning vs. appearance. Then when the counters were being measured I asked about it. The counter installer said it is best in my case, to go with a negative reveal. He took a staight edge and showed that my sink was not truly straight. That would be very obvious once you placed a straight edge of granite (in my case quartzite) around it. So in my case having a Blanco sink, which I love, was just off enough due the nature of the material/manufacture that it would have looked "off". I went with a negative and I think it looks awesome. Here's are pics but the lighting isn't great. Also, when mine was just sitting in the base waiting for the counters...it was obvious that it was in place to be under mount. I'd definitely be questioning your installer/contractor just to be sure.