99% of stuff (if not all) are compatible with it. Some old apps oddly enough can sometimes have no sound on the RG-350 but thankfully all of them were open source apps and as far as my emulators were concerned, i was able to fix them all. (one of them being the GX4000 emulators)
I wouldn't worry personally and you can also use the same toolchain if you want to program stuff on it.
Yes, the PlayGo2 (also known as the Miyoo Max or PocketGo 2) is using the exact same SoC as the GCW0/RG-350.
The difference mostly boils down to the kernel and screen being used. If you want to use the PlayGo2, i would recommend you flash RogueCFW on it right away as he ported the RG-350 kernel to them.
Be warned however that RogueCFW is not compatible with a certain motherboard revision of the PlayGo2...
Honestly, i would just recommend the RG-350 if you don't want any fuss and use the OPK update files to upgrade the firmware.
For my ports, you can get my OPK builds here :https://gameblabla.nl/files/ipk/gcw0/