yeah use plywood counters not formica

"(2) Put in a Kohler tall apron single bowl 36" undermount with the exact same dimensions as my sink on back order. (I won't have to pay for this sink) Finish the countertops, and backsplash. When my sink comes in remove the temporary sink and replace. My contractor seems to think this can be done."

Your contractor is correct. Less than two hours, tops.

This is one time I'd advocate for topical silicone only, none on the flange, for the first install.

I would do choice #2 because I am a single-bowl person, and I think you will be "converted" once you have it. :) Then you are done with your reno and no later changes are necessary.

Also, #1 will be more expensive and messy. While formica countertops are less expensive, they are still an expense. Then, once they are removed, what do you do with them? I hope not put them in a landfill. Perhaps Habitat for Humanity or a similar charity if you decide on #1.

Are you even sure #2 choice is available? There have been several posts on this forum from people unable to get Kohler apron sinks of any configuration due to the fire at the Kohler factory.

I'm definitely a divided sink person. I had a Kohler divided sink prior to renovation and am using a temporary single-bowl sink now. Hate it! I would certainly donate or reuse the countertop, but agree with others that plywood is a better option. I called Kohler and they are saying 8 weeks - however who really knows what the reality of this situation is.

How does it make any sense to hold up countertops and backsplash over a less-than-two-hour low risk job?

I would do choice #2 because I am a single-bowl person, and I think you will be "converted" once you have it. :) Then you are done with your reno and no later changes are necessary.

This is my vote too; however, since you're sure you're not a single bowl person, have you combed the stores in your vicinity to see if ANYONE has one in stock? Tried eBay? Tried every avenue to get the sink you really want?

"Put in a Kohler tall apron single bowl 36" undermount with the exact same dimensions as my sink on back order."

Another vote for #2, BUT, are you sure that substitute sink that you mention exists? In identical dimensions? If the temporary sink is just 1/8" off on any side from the sink you want, the fit in the counter will be messed up. I would do the #2 choice, but with plywood counters as mentioned above. I would wait to install the real counters until the real sink is onsite. Too much risk.

Backsplash should always be last. You never know, once everything is installed, you might change your mind about the backsplash and want something else. That happens a lot. I didn't even look at backsplashes until everything else was in.

(Edited: Just noticed your post above where you say you agree that plywood is the better option.)

Make the cutout for the permanent sink in the permanent top, please. So what if the temporary doesn't look or fit perfectly? As long as it's not leaking, it's fine.