You're off to a good start, so I don't see any reason why you couldn't do all 3 races a year+ from now. Realistically, if you're well trained for a half marathon, adding a 10K the day before really shouldn't be that much more difficult. Jeff Galloway's plans a great, and are specifically designed for 10K+Half challenges, so that should help; even if you don't use the run/walk/run method, they're a good starting point. I've always taken a very low-key approach to the untimed 5Ks, walking them with my family and friends, so time and cost are the real constraints, not physical ability.
A 13mm pace is just fine and dandy. Looking at the 2017 results, that would put you around the top 40-45% at Princess or Star Wars. You have plenty of time to work on your pace if you want, but you're in a good place right now. If you're able to, find a local race (10K maybe) that you can complete in order to submit a Proof of Time for better corral placement, so you won't have to do as much weaving around slower runners
As for which weekend, a lot of that comes down to personal preference, travel availability, and weather. Realistically, the theme doesn't have a huge impact on the events themselves. You're covering lots of distance outside of the parks either way, with some minor variations on the characters and entertainment along the way; the embellishments and details may change, but ultimately they're just window dressings on the running stuff. All runDisney weekends are very welcoming to new runners, though Princess probably has the highest number of first-timers (and Marathon Weekend likely has the lowest); Princess also has the slowest average finish times of any major half marathon in the country
Weather in April will be warmer than February, but the races are early enough that it shouldn't be a major concern. The last finishers will be done by around 10am, with most finishing hours before then. And given the unpredictability of Florida weather, you could easily have a hot race in February too. In the parks, April has spring break crowds, but Princess is always around a holiday week in New Jersey so they're both fairly crowded (but manageable). April also has the Flower & Garden Festival at Epcot, if that influences things
Between the two courses, I prefer the Star Wars course (though I ran it as Wine & Dine this year; I did Star Wars with a different course in its first year). It gives you more distance in scenic areas, and they're spaced out better to allow you to mentally work toward benchmarks along the way. With DAK's extensive backstage areas and the Boardwalk area, you get extra distance of noteworthy stuff, even if you're not really in the parks. The final 2-3 miles is the same as the end of the Marathon in January, which is one of my favorite parts of any course I've ever run (Disney or otherwise), passing along Crescent Lake and going the long way around World Showcase. The 10K course is pretty boring until around mile 4, but is great once you get to the parks
The Princess course is the same as the Half Marathon (and first 9+ miles of the Marathon) in January, and is okay, but I'm just tired of it. You get about a mile in MK and half a mile in Epcot, and most of the rest of it is along relatively unremarkable roads and parking lots; there really isn't much park time with this course. It's designed to use wide roads (though there are a couple bottlenecks) to move huge volumes of runners. Unless you really need that photo in front of the castle, it's just not the most exciting course Disney's ever done. The 10K through Epcot similarly has a lot of time on the highway in the first half, but a decent amount of park time in the second half.
Personally (as a male who wasn't a first-time runner), Princess is my least favorite runDisney weekend, by a long shot. There's just a huge atmosphere of entitled amateur hour, with lots of stress about frivolous things while ignoring common race etiquette. Unsurprisingly, but humorously, there are also huge waits for the pre-race port-a-potties. If it were my first time or if I were a woman on a girls trip, I might feel differently, but it just wasn't for me
I'm not a huge Star Wars fan, so most of the theme that weekend was lost on me, but they did a nice job with it. It felt like other runners (even the inexperienced ones) were better prepared for the event and knew what to expect, and there was an appropriately serious-but-festive atmosphere. My friends who are bigger Star Wars fans definitely enjoy it, and overall I think it's got a lot going for it. It doesn't get as much attention as other races in the rD lineup (which may change with the cancellation of the Anaheim races), but it's a really solid event
). The Princess Half was chosen for the category "best first half marathon".