1. Looks like you won't need the L28et ignitor, you will be using the IGBT on the megasquirt board to fire your coil.
2. Sounds like you got it, just connect the resistor between 12volts and where the GB wire connects to megasquirt.
3. 18awg should be fine
4. Run half of the injectors from each pair of wires. Like injectors 1,3,5 on 32,33 and injectors 2,4,6 on 34,35. That spreads the load on the fuel rail, but I don't think it really matters how you group up the injectors. Look through the MAP sharing sticky to see how people set up their injectors (usually alternating vs simultaneous).