Milan airport hotel and transportation to Varenna recommendations

There is a Sheraton hotel right at Terminal 1, or a Moxy (Marriott property) by Terminal 2. You will arrive at Terminal 1, but there is also a train station at Terminal 2. Moxy is likely the lower price option, but you should check both.

If willing to be 15 minutes away, the Villa Malpensa has a terrific restaurant, and of course a shuttle.

However, you might find it far more enjoyable to take the Malpensa Express to Milano Centrale, a hotel near the station or easily reached by Metro. The Duomo is four stops away. Have a nice dinner; walk around town.

I also encourage you to spend the night in Milan. Stay at the airport when you have an early flight, and we usually stay at Villa Malpensa.

I haven't check but I don't believe there is a train from the airport to Varenna. You would take the train to Milano Central station and change to the train to Varenna. The are a number of nice hotels within easy walking distance of Central. I would stay near the train station. Just one less hassle in the morning. There is no advantage to staying near the airport as it just increases your travel time for the next day.

The central train station is over an hour from the airport (assuming Malpensa) by train (from the airport train station) so you might as well make the trip to Milan that evening to save time the next morning.

The Central station is 52 minutes away by train from Malpensa's Terminal 1.

I can't get why would you waste a night close to an international airport why ypu could stay either in Milan or in Varenna. What's the pro?

Wow these are all great replies. To be honest i hadn't really thought about taking the train into Milan and staying there overnight. That seems like a great option and I will start looking for hotels near central Milan and the train station.
Any other suggestions for things to do in Milan in the morning before heading for Varenna?
Thanks again to all who have replied.
Bob

6pm is not that late. You can be in the city by 8pm, check into a hotel near Milano Centrale station, have a dinner, and the next day you complete the second half of the trip. Milan is generally lively at night (although in August many leave town on vacation).
To make it to Varenna on the same night, you would need to catch the train at the airport at 8:07pm. That’s the last one that can get you to Milan Centrale on time to catch the last train to Varenna. Making that train is possible, although a delay on your flight might make that difficult.
Trains to Milan Centrale run until past 1am

I would visit the duomo. It is walking distance from the area by the train station.

Being as you will want to be at the hotel in Varenna by 4 pm to check in and be at the 5 pm meeting with the group, you will need to be on the 2:20 pm train at the latest. There is no train at 3:20 pm. Takes 1 hour to get there.

In august I'd pick an hotel close to Milano Cadorna station, even if the following morning you will have to take the metro to Centrale.

Cadorna station is served by airport trains, too. The Train ride is 20 minutes shorter and the Navigli neighbourhood is full of restaurants and bars.

We stayed at Hotel Berna: https://hotelberna.com/en/ for our one night in Milan. It is easy walking distance to the train station, clean and has an amazing included breakfast.