Northern Italy by train in late April to mid May, then a week at Lake Garda

I think you can likely consolidate several of those into one base and do day trips, unless you especially wanted to experience different ones at night and don't mind the moving. Given travel time, Urbino will definitely be a separate stay.
It could be that train schedules are just not posted yet.

The complete train schedule for April is not out yet. There will be trains, no worries. Look at a schedule for later this month to see what normal schedule looks like. It does not change all that much.

Where is your apartment on Lago di Garda?

Trains only serve two stations at the southern end of the lake, Desenzano del Garda ands Peschiera del Garda. Both are on the main line between Milano Centrale and Verona, and are served by both fast trains (Trenitalia Frecce trains) and regional trains. From either of these towns, you can reach most other towns along the lake by ferry. Or bus.

Last September we took the train to Desenzano, then walked down to the ferry dock and took the fast boat to Salò, an hour away. After a very pleasant stay there, we caught another fast ferry for the one-hour ride to Malcescine, our next location. These fast ferries make fewer stops than the slower boats, and honestly are not as nice to ride. There is no outside seating, and the few window seats are not all that great because the windows are subjected to constant spray and are not all that clean. The seats in the very front are OK but you will only get one of those if you are near the front of the line at the very first port for that boat.

hey hey peter.riskind
as Lola asks, where are you staying on lago di garda and if it's your first time to the lake? the lake is gorgeous, we stayed in bardolino at hotel nettuno. lots of germans/austrians there. we drove from venice for their annual wine festival (festa de'll uva) late september/early october. lots to see and do on the lake. see if other events are happening while you're there
visitmalcesine.com
lakegardatravel.net
click town guides and read about what they offer. you can look at getyourguide.com (a reseller we have used in 4 cities without issues) to see what there is. always look within site if there is a website of company that runs it and book thru them
duetigarage.com
look at trike rentals for a tour around part of lake
rossiwrites.com/ best towns on lake garda
earthtrekkers.com/ lake garda bucket list
25 things to do on lake garda
annascookeryschool.com
take a cooking class. you can stop at a tourists kiosk in piazza to see if anything is offered for that day
many vineyards and wineries around the island to tour or wine tasting plus many olive gardens to taste olive oil
just some info for you to research before your trip. if you do rent a car, you will need and IDP (international driving permit).
AAA.com/IDP apply for one or stop in a AAA office. good for one year. have fun and enjoy

If you are departing from Milan to your home, consider shifting your vacation a little bit to early May to late May and look into finishing your trip to include the weekend of Piano City in Milan.

Piano City dates are May 23-25, 2025. The shift will still accommodate your schedule at Lake Garda, though it may complicate the well-considered loop that your destinations imply.

This is a festival we encountered in 2015. We were concluding out trip to Italy with three nights in Milan and I was a little annoyed at myself for setting 3 nights in Milan at the end - one night too many, I thought. But on our first night, a local couple we encountered as we were heading to our hotel mentioned Piano City to us. And so, we spent the better part of two days and two nights listening to jazz and classical music in one of the city’s parks - when we weren’t at the Duomo, the Last Supper, the Galleria or the Biblioteca and Pinacoteca Ambrosiana.

Piano City is throughout the city, even if three of the main venues are in a single park. See https://pianocitymilano.it/storia/?_gl=1*mvhs6u*_up*MQ..*_ga*Mzk3NTcwMjQ4LjE3MzE3ODYwMTQ.*_ga_FFT68C453R*MTczMTc4NjAxNC4xLjAuMTczMTc4NjAxNC4wLjAuMA..

Through the years the festival has searched for new and unconventional venues to describe the city: the imagination has taken pianos onto trams and rooftops, down in the streets on top of the Piano Bici and in the channels on ferryboats.

Every year the pianos invade homes, courtyards, squares, parks, museums, terraces, schools, transforming the city in one grand outdoor stage.

And so, our not-so-well-planned final two full days in Milan turned into an absolute delight … even though we didn’t manage to get on the tram with a piano.

Buon Viagge.