How to make custom roms for chinese android tablets ?

Hi,

I bought several chinese tablets and finding firmware for them will probably be as impossible as finding the manufacturer

I would like to build my own vanilla android firmware from the source (I guess it can't be worse than the Linux from scratch thing, which took ages!)

I would like to know, roughly, what is the process like for something like this ?

is there something like gentoo that is half-automated and lets me tune most build time parameters to my liking ?

for reference the tablets are

noname epad 7" (800 mhz, 256mb ram, 2gb nvram, one miniusb port, runs android 2.3.4, resistive 800x480 lcd) 70$

"Fly Touch 7 V10" (1.5ghz, 512mb ram, 4gb nvram, two usb ports, ethernet port, 10" 1024x600 2-point capacitive lcd, runs android 2.3.6, builtin gps with external antenna) 170$

(didn't receive the ones below yet)

Cube U9GT2 (RK2918 1.0GHz, GC800 GPU, 1gb ddr3, 8gb nvram, 9.7" IPS 1280×768 screen, runs android 4.?.?) 238$ ebay item number 260966528657

Ainol Novo7 Paladin (A10 cpu unknown speed,GC860 GPU, 512mb ddr3, 8gb nvram, 7" 5 point capacitive lcd, runs android 4.3.3) 120$ ebay item number 330684897630

unknown brand "A2000 rz" (MTK6516 416MHz + 280MHz(?), GSM quad band radio dual sim, 512mb nvram, 256mb ram, 4.3" 800x480 resistive lcd, built-in gps) 123$ ebay item number 150775056674

none of these devices have builtin bluetooth (or even support, except the phone one), I also want to add cifs mounting support (so I will need kernel modules added) that's why I want to build my own android roms

any tips, links, etc. would be appreciated

thanks !