1. Which maps do you recommend? Garmin's City Maps, Velo Maps, or Adventure Cycling's GPS map data?I use Garmin City Navigator. Unless you already have purchased maps, invest a few minutes testing Open Source Maps. There are detailed instructions on how to install them. Read the rest of the post for some notes about these maps.
OSM seem to be also the source for Velo Maps.
The ACA GPS map data are just that: routes and points of interest. Use them with any of the maps above.
2. If anyone has done a long trip with the 800, how often did you need to charge it? And how did you go about it?I have toured with the Edge 705, charging it nightly. It comfortably worked all day, close to 12 hours. I charge it from electric outlet when available, or one of the battery charging options suggested earlier.
I found these charging options serve dual purpose to charge the phone as well.
3. Did you set up a trip using Basecamp or anything like that?Basecamp is one option to use, especially with Garmin City Navigator maps. There are plenty of web sites for charting routes, such as Ride With GPS, GPSies, and Map My Ride.
Many web sites offer using Google Maps to display & route on bicycle trails. In this case, make sure to export the route with detailed route points (bread crumbs), not just way points.
4. Overall, how accurate were the maps?I think where the data exists, the maps I used have been accurate. I did find some misalignment when I tested OSM maps, but that was easy to recognize.
5. Would you recommend that 800? I love it as a cycling computer.You already have the unit—give it a try. It is small, light, & familiar to you.