How much time to do I need to factor into my 10k and half marathon runs (for photos (alone) and with characters)?
That's a tough one to answer. Really depends on what characters you would want to stop for, and what your estimated pace would be. On World Drive, shortly before the MK toll plaza, you can get in line for characters on your way to the MK, but then see how long the line is again on your way out of the MK. I've stopped for a picture with about 4-5 people in line on my way in, but seen 40-50 in line on my way out. Figure even if they are only taking 20 seconds per person, that line would still easily take 10-15 minutes. Admittedly there were probably several groups in that line, so it wouldn't have been quite that long, but still give you an idea of the ranges. I'd suggest looking over race reports from past races to get an idea as to what characters you might see. Some years there have been lists available at the expo, used to be at MarathonFoto, no idea if Photopass will do anything similar. Then prioritize based on the character and what your pace is. For instance, I've taken a 5 minute wait to see Oogie Boogie, but wouldn't wait more than 30 seconds or so for Stitch.
runDisney suggests shooting for at least a 15min/mile pace to allow time for characters, I'd suggest shooting for 13/14 if you can as a much more realistic pace based on the waits I've seen.
've read that the bus lines returning to the hotels are long, if I finish the half in 3:30, how long should I expect it to take me to return to my room?
Once again, tough to answer. They usually are pretty good with trying to get people out of there as soon as possible. I think that All Stars usually has a pretty long line might take 4-5 buses to clear out, but most of the others are usually only a bus or two. I've never had to wait more than 10 minutes or so to be on a moving bus. But once on the bus, it can still take another 10 minutes just to get out of the Epcot area and on the road. 45 minutes should be on the safe side, maybe some other people can chime in with other guesses.
How long should I expect to be at the expo? I'm not buying the running shoes, is 3 hours enough time to get my packet and make it through the expo if I'm planning on going Thursday (probably arriving between 11:00 a.m. - 1:00 p.m.)
Depends on when you go and what you want to see at the expo. If you just want packet pick up, you should be able to be in and out in 30 minutes or so, unless there is a long line waiting to get in. If you want to look at 5 booths selling sparkly skirts, and 4 selling different energy bars, and possibly buying race merchandise, then it could take a few hours. But 3 hours should be more than enough unless you plan to do some serious shopping.
I'm planning on running in short sleeves, should I do a gear check for my jacket or are those lines too crazy?
I've never found the lines to be ridiculous. Just don't wait until the absolute last minute before going to gear check. The pick up is pretty spaced out naturally from the runners, but drop off can get hectic if you wait until everyone else goes.
However, gear check should really be looked at as storage for stuff for post race. You will most likely be leaving the bag check area at least 30 minutes before the race starts, and then depending on your corral, you may not start moving for another 45-60 minutes after the first runners go. So you might be without your jacket for 60-90 minutes. If you are worried about being cold you would most likely want to either bring throwaway clothes, or look into sleeves. Throwaway clothes are pretty much any piece of clothing you would wear, and then toss into the donate bins just before you go. Old hoody, race shirt from a race you don't care about, etc. Sleeves you could start off wearing during the race, and then remove and carry/tie around belt/stuff into wasteband etc mid race when it warms up.
Edit: Replaced throwaway for the word that apparently gets bleeped out here
) t shirt", I don't need anymore merchandise since I preordered pins, etc., at registration.