Awe, you sound so much like me! A younger version haha. I too spent time in Italy during college, and my husband has an Italian background on his mom's side but has never been. We are going next month and I can't wait for him to experience it.

I would break it up like this.

5 days Rome - This will be amazing for him (I assume he is also Catholic like my husband). Really soak it in.

Amalfi Coast - a night or two? I haven't been for long, only on a day trip to Pompeii.

5 days northern Italy - Venice (2) and Lake Como (3). If Venice is not a must-do for either of you, skip it or just make it a one-night stop and add a night to the Amalfi Coast.

5 days Bavaria - (base in Munich and do day trips to Fussen to see Neuschwanstein, Garmisch-Partenkirchen,
Dachau, Salzburg) .

I think you should choose EITHER Munich OR Switzerland... give Italy the 10-12 days it needs. You'll get your beautiful Alpine mountain experience in either one of those.

I don't think it's too much to do Italy + one of those countries and I think they would be a great complement to one another! Lots of varied experiences, sounds like a great trip no matter how you do it.