Wanting to try out MMDVM on the Pi, I came across a distribution called Pi-Star that is excellent and extremely simple to set up. Brilliant work by Andy Taylor, with responsive Facebook support group.
Have used with a Pi2 and Pi3 in combination with DVMega BlueStack connected via USB for several weeks now.
I have added a Nextion 2.4″ screen that I purchased a while ago but was still sat in its box. Using these instructions, I was up and running displaying modes and callsigns in less than 30 minutes! It connects via the Pi2/Pi3 IO pins. Brilliant.
Update: Pi-Star supports DVMega boards plugged onto Pi2/Pi3 IO pins OR via a BlueStack configuration. If using the DVMega board on the Pi, the Nextion screen will need to connect via USB using this USB 2.0 to TTL Module Serial Converter adapter. If using USB to connect the screen, follow the same instructions above but replace /dev/ttyAMA0 with /dev/ttyUSB0 in the Nextion Port setting of the initialisation file.
Note: The Nextion 2.4″ screen is now available (since July 2017) in the UK from ML&S.