Don't force your child to have pictures with character if your child seems scared. At that age, it's often more about the parent than the child's wishes
Take it slow, take it easy and take frequent breaks. 

Afternoon breaks are important for us. We can maybe go the 1st day without one, but we'll be feeling it the rest of the trip. We get there early and come back around 5. Collect FP's in the morning for use later when you return.
Get there at RD to avoid waiting in long lines. My little one wants to wander around, so keeping her in line for more than 20 minutes is a chore. If you do get in a line, have snacks and drinks ready.
Take advantage of rider swap.
We never went back to the resort for naps. The kids napped in the stroller and we browsed Epcot's World Showcase or something like that. You can ride the monorail over from MK without taking them out of the stroller. (You have to take them out for the bus.)

Not to sound dumb, but what is RD? Lol.
We took our daughter for her 1st trip last September, she was 22 months old. We had a great trip! We followed the UG's recommendations for park days and for our touring plan. It will be HOT in September - we went the very last week hoping it would be a bit cooler. So definitely something to plan for. Our DD was able to nap in her stroller - I was really relieved b/c I hate the idea of going back and forth from park to resort, especially at MK where you waste the most time in transport. Although we will have to do it when she is old enough for the night shows/parades
The best use of your time will be to get there early. And if you aren't interested in creating a touring plan, at least have an idea of the rides and shows that your DD will enjoy. We ate breakfast in the room most mornings to save time, that way we could let her sleep in a little longer.
Which parks on you going to?

I say go early, take a cool down afternoon break (nap) at resort, (maybe between 1:00-4:00) then hit the park again after 5 when it is cooler. Maybe even take stroller and hit a few evening EMHs and baby can sleep while you and DH enjoy some romantic strolling time.