crowds in northern Italy in May

Others here will be able to provide current information. I cannot, though I have been to almost every place you mentioned. I've read serious complaints of day-time overcrowding in all those locations except Lucca and the lakes.

But please bear with me while I pontificate. I think there are three possible responses to credible reports of severe overcrowding:

1. Skip those places; go elsewhere. (But they are wonderful, and they are not going to get less crowded.)

2. Go, but give yourself enough time in the problematic cities so you can explore less-busy corners rather than rushing from one massively-crowded sight to the next. This will give you some crowd-free down-time.

3. Don't build your entire itinerary around the most over-visited cities; include some less-trafficked spots as well so you're not fighting crowds everywhere.

As I'm sure you can tell, I favor Option 2 and Option 3. Places I visited in Italy during May-June 2015 that didn't send me running for the hills: Padua, Vicenza, Ravenna, Bologna, Assisi (away from the basilica), Puglia and Sicily (but Taormina is a problem). I also went to Rome but did a lot of simple wandering around and didn't feel hemmed in by other tourists.

Edited to add: One thing about the Cinque Terre: In recent years two of the four most popular trail segments between the towns have been closed because of storm damage. We haven't heard that they are scheduled to re-open soon. There are other hiking possibilities in that area, but I think they are higher up, meaning even more stairs to climb before you can start walking. There are other pretty coastal villages in Liguria that might be substituted. I'm sure other posters can suggest a few.

You have raised a number of issues. First, a simple one. May 1 is a national holiday. Don’t include it or days around it in your plan.

Your points #2 and #3 seem like reasonable ideas to me. A base in Tuscany would allow you all to see a lot without too much battling of crowds. San Gimignano to my taste, is horribly overrun with tourists and doesn’t have as much of interest as some of the other towns, e.g., Lucca, Arezzo, or Volterra.
Venice is big enough and important enough to warrant putting up with crowds. There are a number of world-class sights; and if you wander off the main drags, it’s easy to enjoy the ambience free of other tourists.
As for the CT, the crowds are the most note-worthy thing about them. I wasn’t blown away by them on my first visit (2001). My brother and sil insisted on a visit a couple of years later because they wanted “to see what all the fuss was about.” They hated it. First weekend in June, the crowds were unbelievable.
There are plenty of less crowded places in the Lakes area, where you can enjoy magnificent scenery and do some hiking.
One unsolicited piece of advice: I assume you will be renting car(s). Get at least 2. For one thing, any car large enough for all of you would be too unwieldy on most of the non-autostrada roads. Secondly, more than one car will give all of you the flexibility to pursue different agendas if everyone doesn’t want to do the same thing some days.

Very sensible advice. Thank you. We would not be in Italy on May 1 holiday anyway but thanks for the warning. I will look into Arrezzo. Is it a place that you would spend a whole day or combine with another hill town? Years ago we went to Sienna and were well amused for the day. But I have since read about people going to multiple places in a day. I am unclear if Sienna had more to see or if different style of traveling.

I have thought of Verona and Padua. And I think you are right that the key is to not go entirely to crowded places. But trying to balance that with what you might give up isn’t easy (except perhaps for Cinque Terre).

I realized when reading about the trail closings in Cinque Terre that my colleague had been there prior to that. She and her husband had hiked between towns. So perhaps better to substitute another place? And as you both suggest, it might be the kind of place that isn’t worth fighting the crowds to see. I had thought perhaps either Lake Como or Lake Garda. Thoughts on accessibility and availability of rentals that can accommodate 6 people? We also could of course stay in a hotel but in my experience about 1/3 more expensive.

I was thinking combination of trains and car rental. Driving provides more flexibility but is more stressful in a foreign country. We drove in Greece (but not in Italy). In santorini, we ended up with two cars rather than the van we had reserved for the day and thought it was much better for the narrow roads. We actually changed our van rental to two cars for the main land (after reserving it 9 months in advance!).

About 4 years ago, I was in Bologna, Florence, Assisi and Orvieto in mid-May. The only one that was at all crowded was Florence and that was only around the Ponte Vecchio and the streets leading into it that were really packed with tourists. I was there on the weekend, which may have made a difference. The Boboli Gardens weren't crowded or the Pitti Palace, or even around the Duomo.

If you avoid Rialto and San Marco in the middle of the day, Venice isn't crowded either.

Cinque Terre - well, that's less likely to be pleasant. But some here have suggested going to other towns on the Italian Riviera instead.

I spent two weeks in Orvieto in late May/early June 2015. I liked it a lot, but there were times when the main streets in the central part of the old town (in the vicinity of the cathedral) were quite crowded. I wish now that I had paid attention to how the tourist flow varied by day of the week. A lot of the tourists were Italians, and I think mid-week in Orvieto may well be quieter than Friday-Monday. But it's a lovely place in any case, and you can get away from the crowds if you just walk 2 blocks away. For me it has more than one day's worth of sights.

Siena, like Orvieto, is an example of a town that isn't just a 2-hour stop. A good guide book will usually make the distinction clear. If in doubt, skimming the Things To Do list on TripAdvisor will usually allow you to determine the difference between places visited primarily because they are picturesque and places visited because there are many sights one might want to go inside. A lot of picturesque places are worth night just to enjoy the atmosphere after the day-trippers depart, but few of us have time to spend one night in each of those places--and a string of one-night hotel stays is tiring, anyway. Having a car makes it possible to hit 3 or 4 nice small places in one day--something that's nearly impossible to do via train and bus.