I can help you.
The GUI should work perfect once you have your controls properly mapped but that device doesn't have an autoconf yet.
First of all, what version are you using? if you're using the playstore version I recommend to remove that and install from F-Droid, info on the subject here:
http://www.libretro.com/index.php/new-nightlies/
Now about your issues:
- CRT shaders on that device... highly unlikely, maybe CRT-easymode (the non-halation variant) or crt-hyllian, but the screen is small and not really high resolution so even a basic scanline shader should look great with integer scale
- Crashes, can you tell me what causes it to crash?
- UI elements not working: which ones, can you take a screenshot? is your UI green/black or the new one that emulates material design?
- Make sure you set your save locations and BIOS locations to user writable locations from the get-go, otherwise you might lose your data if you uninstall (the default location is with your roms but that isn't always writable)
As for controls, to remap your inputs do the following:
- Navigate using the touchscreen to Settings/Input/Input User 1 Binds
- Select user 1 bind default all
- Select user 1 bind all
This is where it gets tricky. In RetroArch we handle each device as a controller, so the first device to be active is mapped to port 1 (like a console), so hopefully your device has the controller implemented as one HID device (several controllers don't do this, NVIDIA shield has the back button in a separate device, ARCHOS gamepad is 3 devices and so on), you should see a different name appear when you hit a button if the device is different than the current device and on that case we'd have to add a workaround for your device.
- If everything mapped you should be set, otherwise edit the binds that failed (or clear them pressing whatever you bound as start)
- Select User 1 Save Autonconf
- Select user 1 bind default all
If your device has a sane gamepad that should be it for this part, if not let me know, I've added workarounds for some other devices already.
Known issues:
- The overlay reappears when you task switch
- The stubbed android menu is still present and confusing