Yes, you have to pick up your own bags but there's very few flights coming in at that time so they come through pretty quickly. While we've always liked having our bags picked up for us and arriving in the early afternoon, the evening flights have worked out for us. Yes, we get to our room really late (really early?), but we sleep in the next day and get a full day in. If we come in the afternoon, I have to take an extra day off work and still only get a partial day in the parks. It was also really cool the one time arriving at WL with a totally empty lobby - got some really good photos then with nobody in them.
It depends on how many people are already on the bus when you arrive that late. One time we were basically the last people to get on and left immediately, other times we've had to wait 30 minutes or so before it leaves. I just nod off as soon as I get on and wake up at the hotel. The good thing is that you don't have to stand and wait. There's a bus waiting and it just takes whoever arrives and then goes to all of the relevant resorts. Last time the bus driver told us (take that for what it's worth) that he's supposed to wait for 45 minutes or until the bus is full, whichever comes first and then head out. Traffic is pretty light at that time so it's not likely to be more than 90 minutes which is pretty much the same as during the day. If you arrive on time, you'll be in your room probably by 2:30-3:00 am at the latest.