I apologize in advance for the length of the post--I didn't want to leave out any of the good stuff!
Let's start with San Juan! We stayed at a Hotel Cervantes in Old San Juan, which is the older part of the city and very walkable. I would recommend staying in this area if you don't plan on renting a car. We were really happy with the hotel, the service and the location. There are lots of historical sites, as well as several vegan-friendly restaurants and bars nearby. Here are just a few photo highlights of that area.
Below you can see our meals starting at Milwaukee's Mitchell International Airport. Concourse C has a French Meadow Bakery with vegan chili and several bakery options. While in San Juan, we had a very limited time to accomplish all our touristy goals, so we ended up eating twice at Cafe Berlin. We were really pleased with the food and service we got there--the waiters absolutely understood what vegan meant and were happy to point out our options. See the individual images below for details on our food.
You will also find that you don't need to know Spanish to get around Old San Juan. Most everyone there speaks English. The only time I needed to use my mediocre Spanish skills was on the cab ride from the airport, but I'm sure that's something that could have been worked out in English, depending on the driver.