We have never gone to an AI and are a bit apprehensive but want to give it a try. I am leaning toward Punta Cana. And possibly Excellance or maybe Iberostar or Zoetry. The Adults only is interesting. I would like a resort with a good number of restaurant options. Looking for good food a must. Any suggestions and is Punta Cana where I should be looking?

All three of the resorts you mentioned are wonderful. The Iberostar Grand is part of a much larger complex.
Do you want a BIG resort or a smaller one? Zoetry and Excellence are smaller.
You can't go wrong with any of them.

Excellence or www.dreamsresorts.com

La Romana for me...

puntacana.com Hard Rock new nice for casino/party

bookit.com/dominicanrepublic/puntacana/hotels/hard-rock

It sounds like the OP wants an adults only resort. Hard Rock is NOT adults only nor is Dreams or La Ramana.

what is important to us is good food and decent drinks. Even if tipping or paying extra is required. Not afraid of a large resort if that would mean more choices of restaurants.

Also I have heard that at Excellance there is a dress code for the restaurants. That is not an issue for us and actually like it but exactly what does that mean. Jackets? or just dress casual collard shirt which we would do anyway

The dress code is just long pants for men in the ala carte restaurants for dinner. No real "dress up" clothes are needed.
At the Iberostar Grand you need to make reservations for dinner, but have a concierge to do that for you.
At Excellence you just go to the restaurant. If they are busy, you wait until a table opens. We never had to wait when we were there.