Don't complicate it:
*Use RFR lines - more capacity, better for express operation
*Use AC traction - eventual expansion to Geelong
*Use Southern Cross - better for information purposes and capacity
*Stop at Sunshine and Footscray - or otherwise useless for west
*Run buses during the early hours period - no point without other suburban trains
I agree with your idea sir.
No point running 24 hour service, given between last and first train on the current Metro time table the number of weekday domestic flights arriving/departing would easily be less than 15, and international flights arriving/departing would be less than 6. Unless they are going to take the Metro system to 24 hours.
Having a couple of stops makes sense for those western suburban dwellers, so they don't need to go in and out of the CBD to get the train, otherwise those people are more than likely to continue driving.
Even stopping at SXS makes sense, you can get a train to just about anywhere from there, and if you needed to get to Flinders Street you wouldn't be waiting long.
In my travels I have used the rail connection at Sydney, New York, San Francisco, Vancouver and Chicago and a system like this suggested is similar to these locations and I feel would give good value for money and be well utilized.
Not sure Skybus, the taxi companies and the parking companies would be too impressed with the lost of patronage tho.