Hi mate,
I like your idea of a built up unit it's been something I've been meaning to do for a while - take a look on Tindie I'll be sure to get something up there soon.
Rabbit ECU project isn't amateur. I've been designing and building ECUs for 20 years. The original Sparkdog SDR, Hydra Nemesis 2.5 and 2.6, GP-meter 6.0 and now I'm developing the Rabbit ECU for DIY highly integrated systems needing direct injection, drive by wire and CAN networking for DSG, etc.
I don't know why you are mentioning that other product so much. The Rabbit ECU integration into the Mk6 GTI needs the following:
1. Fuel pump PWM signal
2. LSU4.2 5 wire control
3. Coolant pump out relay control
4. MAF input (frequency input)
5. ECT input (analog with pullup)
6. ETC motor output+
7. ETC motor output-
8. ETC input throttle position main (analog)
9. ETC input throttle position sub (analog)
10. Igniter output cyl1
11. Igniter output cyl2
12. Igniter output cyl3
13. Igniter output cyl4
14. Crank sensor input (frequency)
15. Knock input (analog/frequency)
16. RPS input (analog)
17. Charge pressure sensor input (analog)
18. Intake runner output (PWM)
19. Rail pressure solenoid output (PWM)
20. IAT input (analog with pullup)
21. ECT input2 (analog with pullup)
22. GDI output+ cyl1
23. GDI output+ cyl2
24. GDI output+ cyl3
25. GDI output+ cyl4
26. GDI output- common1
27. GDI output- common2
28. PPS input pedal main
29. PPS input pedal sub
30. Recirc valve output (PWM)
31. Wastegate valve output (PWM)
32. VVT cam phaser output
33. CAN+ for body and DSG comms
34. CAN- for body and DSG comms
35. 5 volt sensor ref outputs
36. 5 volt sensor ref grounds
37. Power grounds x 4
38. Power feeds x 2
39. Motronic relay
40. Shield grounds x 2
41. VVT cam position input (frequency)
42. Voltage boost input
If you want to be fussy you can also add
43. Intake runner input (analog)
44. Oil control valve output (PWM)
45. Post cat sensor (4 wires)
I'm guessing that's up over 60 wires of the Rabbit ECU 80 available pins. I don't think you are comparing apples with apples, but I'll leave comparisons for others like I said.
The PCBs are assembled on an automated line same as every other electronic device and the PCBs are bare board tested and AOId. So it's professional.
The pricetag is what it is - parts, PCB manufacture and assembly isn't cheap.
Most importantly I'm having fun with this projects here is a video of the GTI :-)
youtu.be/4YZl8tuLx_4