So, a few other caveats and things to note...
In terms of the "see both parks" I mean, how in-depth do you want to experience both parks. By eliminating the character meet & greets, that will help save a lot of time, but there are still the shows (e.g. Royal Theater, Mickey & the Magical Map) and street performances (e.g., Dapper Dans, Five & Dime, Newsboys) to consider. I think three days is enough to get a good sense of the parks, but it's probably not enough time to do all of the rides and see all of the shows. So, I would still do some prioritizing beforehand, so you can see the things you want the most.
In terms of the nighttime shows, it's worth noting that prior to the start of the 60th Anniversary Celebration, fireworks were only presented on weekends (Fri to Sun) outside of the peak seasons. It's not known if they'll go back to the weekend only schedule after the 60th Celebration official ends or not. Also, it's not quite known when the Spring Break season (usually considered peak season, with nightly fireworks) will start/end in 2017. WoC is usually presented nightly. We don't yet know what Paint the Night's schedule will be after the 60th Celebration ends, either. Just some things to keep in mind because Easter is in mid-April in 2017, so the schedule in early April may be very different from the schedule in late-April.
In terms of FPs, at this point, DLR is still using the "Legacy" FP system. You can also check the official
Disneyland App, which will give you the current return time. Unlike WDW, there is no official grace period (either early or late), so plan on returning during the time window printed on the ticket.
Once you've obtained a FP, you can collect your next FP two hours later or when the FP window opens, whichever comes first. Let's say it's 9:00 am and you obtained a FP with a return time of 10:15 am to 11:15 am. You'll be able to get your next FP at 10:15 am (when the time window for the most recent FP opens). On the other hand, let's say it's 9:00 am and you obtain a FP with a return time of 2:15 pm to 3:15 pm. You'll be able to get your next FP at 11:00 am (two hours after you pulled your most recent FP). (Caveat: You cannot hold two FPs for the same attraction, so if you already have a FP for an attraction, but it's time window has not yet opened, you cannot get another FP for that attraction even if you're eligible to get more FPs.) A few other notes:
- 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. Likewise, WoC FP is also a "disconnected" FP. 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/