I have only work for gpd xd and q9. Both with rk3288 chipset. They have different partition layouts though. Xd uses unified storage and q9 doesn't. Screen resolution is different Too. No idea about cwm with touch controls.
System.img is created in ext4, it's transformed to ext3 after using rk3xxx tools to add a couple of things. It's a rk3xxx tools issue. If you use it It will be transformed to ext3.
About system.img generated by firefly, you need to add things from stock firmware, like framework files and systemui.apk, and also gamepad.apk and the files under system/usr/keylayout. With that It should work. You may also need to modify build.prop to spoof yo Nexus if you want. And edit a couple of more files to get init.d support. Also,, adding the root files, the supersu.apk etc...The Firefly creates a just a base system.img to begin with. If you don't want to complicate things, just take my system.img or a stock one and modify at your own.
About cwm, the problem is that rockchip doesn't use android partition standard, so i suppose must be modified heavily, so not sure if rom.manager or apps like that Will behave well with It. But i haven't used twrp or cwm Too much . I only use twrp un my phone, but i must enter recovery using a button combo ir a reboot APK that allow to reboot to recovery.
Sorry i am.not Too specific, but i madre those ROMs more than a year ahí and after múltiple bricked, etc , so i cannot remember everything to make a step by step guide.