eurail global pass 1st or 2nd class?

The Eurail pass only covers the transportation portion of a night train, you pay extra for a couchette or sleeping compartment, or a seat reservation. So whether it is 1st or 2nd class is irrelevant. The pass is good on trains in Italy operated by Trenitalia. Regional trains don't have seat reservations, so there are no extras for these. IC, EC, and Freccia trains require seat reservations, so you have to pay for these.

so a 2nd class pass is acceptable to book a couchette.

but not accepted at all on the competition train company Italo. Italo only go within Italy.

Have you priced out the pass vs. buying a point to point ticket in advance?

Munich is really a bus trip to Milan, and it's a 7 hour ride. There are no night trains thru Switzerland or Italy to get to Milan.

EasyJet flies into Milan Malpensa Airport, and they should be very inexpensive--1 hr. trip.

Air Dolomiti flies to both Malpensa and Linate from Munich. And Lufthansa flies into Malpensa too.

Munich is really a bus trip to Milan, and it's a 7 hour ride. There
are no night trains thru Switzerland or Italy to get to Milan.

I'm not sure I understand what you mean, but ÖBB has daily (nightly) night trains from Munich to Milan.

Have you looked at how many changes you would have to make?

Doubtful you would get a good night sleep and be ready to 'hit the ground running' when you get to Milan

There is a direct Nightjet that takes a somewhat circuitous route via Salzburg, Villach, Tarvisio, Padova, Brescia to Mllano Rogedo, which is outside of town. It takes 11 1/2 hours and you still need a local connection from Rogredo to Centrale, or from Brescia.

Have you looked at how many changes you would have to make? Doubtful you would get a good night sleep and be ready to 'hit the ground running' when you get to Milan

The answer is no changes- departs at 2010 and arrives at 0747 southbound and 2126 arrive 0922 northbound

But that Nightjet makes 8 stops between midnight and the time it arrives at Milan Rogoredo. I would get very little sleep with so many stops.

the night train is no issue from munich. can i get a couchette with a 2nd class pass?

The answer is yes. You need to book the reservation on the OBB night jet website.

As pointed out, your Eurail Pass is valid going from Munich to Milan when you want to use the couchette option. If I were doing this route, I would use the Pass since I have that anyway, the Senior Global to go by OeBB Night Jet.....absolutely no problems.

Make sure you book the couchette option (I don't need that) as that option does sell out.

can i get a couchette with a 2nd class pass?

Yes, I think so. With a 2nd class pass you can only book seats (or beds in this case) in 2nd class, but if I'm not mistaken ÖBB considers both their couchettes and sleepers to be 2nd class.