Cheapest way to buy is usually Undercovertourist. They do email tickets and real tickets in the snail mail. So depending on how quick, check their prices out. Otherwise, more than 1 day tickets are around $20 cheaper on Universal's website than at the gate.
Most of the restaurants can be booked on your phone, or ask at the hotel. I've done same day, except for Christmas time. That's when I book more in advance. The restaurants are not like Disney, each may only be booked a month or so out. Since they are not all owned by one entity, each has their own time as to far out to book.
Get a map when you first enter, to get an idea of where you want to go. Thunder Falls is one of my go to, as well as the Potter quick services. Check the food stickie at the top, she usually has the most up to date menus. See which restaurants interest you, and go from there.
Again, relax, it's a great time to visit, enjoy the parks, and if a Potter fan, see if you can splurge for a 2 park ticket. Riding the Potter train between the parks is neat. Plus, if you feel one of the parks is more busy, hope to the other. They are only about a 10 minute walk apart.
Since you are not staying onsite. Make sure you give yourself extra time to get from the parking garage, through the security, and into City Walk. While there are moving walkways, it does take some time, and sometimes the security can also have a line, and be crowded.
Have fun, and take your time, sometimes use the single rider, after you've ride to together. I hope you both have an awesome time.
