tlovesdis did a great job answer your questions, so I just have a few other comments.
Can you only have one outstanding FP at a time? If not, is there a limit?
There is currently no limit to the number of FPs you can get in a single day, but it depends on the return times of the FPs you do get. As
tlovesdis said, for most attraction FPs, you can get another FP two hours later or when the time window opens, whichever comes first. So, let's say you get a FP for Space Mountain at 9:00 am.
- Example 1: The return time is for 10:30 pm. This is 90 minutes after you got the Space FP. You can get another FP at 10:30 am because the time window has opened.
- Example 2: The return time is for 1:00 pm. In this case, you can get another FP at 11:00 am (two hours after you got the Space FP). One thing to note is that you cannot get another Space FP at this point (you can only hold one FP for the same attraction at a time).
There are a few other caveats:
- There are a handful of "disconnect" FPs. You can obtain these FPs and they do not limit/impact your ability to get another FP immediately. The only "disconnected" attraction FP is for Buzz Lightyear. WoC is also "disconnected" FPs. In other words, you could go get a WoC FP and then immediately go get a RSR FP. F!, when it was being presented also used the FP system, but it is likely dark for the rest of 2016.
- The two parks are "disconnected" from each other. Meaning you can collect a FP in DL and then immediately hop over to DCA and collect a FP there. For example, if you are in DL and pull a FP for Space Mtn, you can immediately go over to DCA (assuming you have park hopper tickets) and get a FP for RSR.
- Once a park ticket has been used to enter a park, you can obtain FPs in either park. So let's say your party all enters DL in the morning. You can then have one person (aka "the runner") hop over to DCA to get FPs in that park. (It's worth noting, I've only ever done this with park hopper tickets, so I don't know if works if someone had a one-park-per-day ticket). This is one of the biggest differences from WDW when it was still using the Legacy FP system.
- There aren't a huge number of attractions at DLR that use the FP system. Mostly they are the thrill rides and a few of the more popular non-thrill rides. Disneyland.com has a list of the attractions that currently use the FP system: https://disneyland.disney.go.com/attractions/#/fastpass/
Can you select your preferred time for the FP window? If answer to the above is no, my understanding is you walk up to the ride and take a FP. But how far away is the FP time? e.g. if it is 10am, is it possible you can't use your FP until 2pm?
You cannot select your preferred time at this point. You can check the
Disneyland App to see the current return time and try to time it so you get the time you want that way, but otherwise you have to take whatever time is currently being distributed when you get to the FP machines. Yes, it's quite possible to pull a FP in the morning and not be able to use it until the late afternoon or evening. This most commonly happens at the more popular attractions (e.g., Space Mtn, RSR). Please note that DLR does not have an official grace period (either early or late), so plan on returning during the time window printed on the ticket.
Can you get FP anywhere else such as a central area with booths/machines? Or do you have to go to each ride? This would be a pain if you are at one end of the park but want one for another ride at the other side.
Currently you do have to go the physical FP machine to get the FPs. So yes, in most cases you will have to go to the attraction itself to get the FP. Most of the machines are adjacent to the attraction. There are a few that are not within the immediately vicinity (e.g., RSR is located near It's Tough to Be a Bug - not even in Carsland), but most are within sight of the attraction.
Do FPs run out for a ride? If so, then you must need some strategy for the popular rides.
Yes, FPs do run out. For the more popular attractions, like Space and RSR, they can runout well before the park closes. I would try to get those FPs within the first hours of the day.
There are rumblings/rumors that a
version of FP+ is coming to DLR, but it doesn't not seem like the ability to pre-book FPs is necessarily going to be one of the features they're importing from WDW. There have been some RFID tests at Space Mtn in the last few days, and there are rumors that at some point they might implement the ability to get a FP using the app or a centralized kiosk system, but at this point, these are all rumors and not dates have been announced. They're talking about these rumors over in the
FP+ (No More Paper FP) thread.