Milan is the destination of great business visits: there are important public Fairs and Exhibitions that attract million of visitors from all over the world.
The website Fieramilano.it 
has an up-to-date list of the ongoing and coming international exhibitions in Milan.
You can combine a business visit with some relaxing time: using low-cost public transportation you can visit Abbeys, Castles, Lakes, and historic cities that you can reach in one day.
Don't rent a car, you don't need it, and in any case you would have problems finding a parking spot. Use instead the efficient and modern trains of the regional lines that I recommend in my book
The cost is very low because these transportation lines are subsidized by the Regional Government! 
All these destinations are listed and described in the book https://italian-visits.com/products/milan-and-day-trips-to-lakes-and-art-cities together with destinations in the city of Milan.