Short answer: Yes to the bungeecord/minecraft server. No to worldpainter.
Do you plan to have multiple servers for bungeecord? If you only plan to have one server, there's no point in running a bungeecord server. You will be able to run a bungeecord/minecraft server on a Raspberry Pi 3 but don't expect it to run smoothly since generating chunks will push the cpu pretty hard. Other than that, minecraft should run OK.
Even though the raspberry pi 3 has 4 cores running at 1.2 Ghz. That still doesn't mean minecraft or worldpainter will use all of it's cores. Minecraft uses about 2 cores/threads for the main game while it can use other cores for netty (networking). So if you make a cluster of raspberry pi's. Bungeecord/Minecraft/WP wouldn't be able to take advantage of the processing power from the cluster of pi's.
I personally don't have experience with WP but from doing a little bit of research. It doesn't really support multithreading that well as far as I know. I could be wrong about this but I wouldn't expect it to be better than your computer.
One last thing about raspberry pi's. The raspberry pi cpu is an ARM cpu (basically, it's a phone cpu). The only version of Windows you can install on it is Windows 10 IoT and you won't be able to run regular applications on it unless they were compiled with ARM and not x86_64. It's also better to install raspbian (based on Debian which is a linux OS) since it's more optimized for running as a server.
