Going solo can be awesome, I just had half a day on Saturday. As said above, hop and get FP's for rides in both parks, a little more walking, but its not terrible. Much easier to move through crowds by yourself too.
Personally, since this is your first time at DL, I would start at DL. Fantasyland at DL is so different than MK, very compact, plus more rides. PP ride is not all that different, queue is way better at MK. Do Mr. Toad and Alice after and then skip over to It's a Small World. Way better queue at DL, ride is better as well. Then maybe hit Matterhorn, it can be a bit shaky for the back.
I would then grab a FP for Space and then maybe do standby for Star Tours. I would then go to CA and get a FP for Soarin, then do SRL for Radiator Springs Racers. Wait for Toy Story Mania will already be at 40 minutes, but I would do it, then maybe Screamin nearby. I would then check on FP time for Racers, doing the ride at night is so much better. But FP can go fast for this ride at times, so you may have to check on this sooner. Then back to DL for Pirates (way better at DL) and HM (I prefer MK version-love the stairs). Just my two cents.
Now if that half day off starts in the afternoon, you will have to tour a little differently. I would still check out Fantasyland first, but you may have a longer wait for all rides and some FP's may be gone for Racers and maybe even Space. 16th and 17th will both be very busy, but you can still have fun.