You’re eligible to apply:
Who You Are:
• You are a citizen or eligible national of a Visa Waiver Program country.
• You are currently not in possession of a visitor's visa.
• Your travel is for 90 days or less.
• You plan to travel to the United States for business or pleasure.
• You want to apply for a new authorization ...
ESTA is only required if you enter the US by plane or onboard a cruise ship.
If arriving by a land border, you don't need an ESTA, but may need to complete a paper I-94W (you shouldn't in your specific case, in theory).
From the official ESTA site
IF I AM IN CANADA OR MEXICO AND WANT TO DRIVE TO THE U.S., DO I NEED TO APPLY FOR ESTA?
If you are a ...
ESTA materials say that if your application is unsuccessful you should apply for a US visa. That is where you will have the opportunity to say "when and why and explain."
I suspect your chances are fairly good, but if you are not successful you will lose the $160 application fee.
There doesn’t appear to be a rule that says you can’t apply for an ESTA while a B visa is processing. You could try and see if it is approved.
The only risk is if your B is denied then your ESTA becomes invalid, even though it’s on a separate passport.
You should not run into any issues. Your reasons for traveling are valid and totally covered under the ESTA program.
I would just take the precaution of bringing along documents that prove your itineraries (your stays in NY, Toronto, Vancouver, LA, and LV) along with a return flight home. This will just show the border guard that you are genuinely ...
If you leave the US and travel to the Dominican Republic you will be readmitted under the same I94 admission that you received when you arrived. This will cause you no trouble as long as you plan to leave within 90 days of your original admission to the US. In other words the total of your time in the US and your time in the Dominican must be less than 90 ...