ESCs - 20A Blheli S or Blheli 32. Something small if you want to fit it on the arm, or use 2 x 4in1.
Flight Controller - Nothing i could find supports 8 motors. Use what you like, set it up as a quad and split the motor output to 2 ESCs.
Build Instructions.
The hardware allows for a 26mm and 30mm hight top plate. Use the 14mm screws with the standoffs for 26mm and use the 16mm screws with locknuts and standoffs for 30mm height. Use the top plate as a reference as to where the longer screws need to go.