The decision sounds easy to me, fly to Rome and ride up through Italy, into southern france, then up over the alps to switzerland, through switzerland into germany, down into austria, down then back into Italy (dont forget venice), then down the adriatic coast to the southern part of Italy, ferry over to sicily, ferry back to italy, back up the western coast to naples and back to Rome.
What a month and what a birthday present.!
What more inspiration can you want, all that history, geography, scenery, culture, gastronomy etc etc etc
Go for it, and keep us posted on how your planning goes. I am new to this site and i am planning to ride from the UK down to Spain next summer and from what I can gather, all of the information that you need is somewhere on this site.
'Never worry about things that YOU cant change'