Plenty of reading material over here, there's several threads about that family of units:
https://forum.xda-developers.com/and...oid-head-units
AFAIK there aren't any custom ROM's for the Intel based models but there are plenty of tweaks and utilities, at a minimum you should be able to root it and install viper4android which will take care of your EQ. Car Launcher Pro and CarWebGuru launcher are both pretty good launcher-wise.
Not sure on the bluetooth, but I'd suggest a USB OBD2 device like the OBDLink SX...there's probably 1000 threads on XDA by people who can't their bluetooth devices to work. I don't know if Joying does this, but some of the android head unit outfits are known to have code in their bluetooth stack so it will only pair/work properly with their own adapters (usually by requiring the device's bluetooth name to adhere to a specific naming convention, IIRC).