Help with Furrtek servo emu board

Looking for some help with making my own furrtek servo emu board as I’m finally doing a proper consolization and would like to remove the mechanical parts.

I have an adruino I can use but am a complete newbie in terms of actually using it to program microcontrollers.

Would anyone be able to tell me which microcontroller I should get? If I have that info I can probably figure the rest out on my own.

Thanks!