Not a bad itinerary. I would make a few adjustments. Obviously up to you if you stay in Venice for a day or two. I've been five times but when I'm in the area, or flying in, I often add a day just cause I love it so much. On the other hand, sometimes it's not worth the trouble. You could go by train straight to Bologna or another option would be to stop in Padua for a a night or two. Lovely city with a slightly less touristy vibe than some. I would extend the Bologna time and do day trips by train to Ravenna and Parma. The less time you have the car the better and it's not needed for those. On the way to Parma you can stop in Modena - I actually like it more than Parma, but it's on the same train line and the trains are so frequent you can easily combine them in a day trip.
After that I would rent the car, you do need it for San Marino but I would suggest two nights - plan to arrive after 4 pm, enjoy it in the evening and early the next morning, then do a day trip to San Leo, arriving back after 4 again. The next morning leave by 10. That's what we did and it worked out perfectly, San Marino gets horribly crowded mid day but is quite lovely early and late and we loved San Leo as a day trip.
If you don't mind one night stays I'd include Verona en route to Lake Garda. Same technique as with San Marino - arrive mid-late afternoon and enjoy it with less crowds in the evening and early the next morning and get out of there by mid morning. You'd probably need to find a place outside of the center since you'll have the car, but the bus system is pretty good.
On Lake Garda the only thing I wanted to see that wasn't at the north of the lake was Sirmione but maybe if you over-nighted in Verona and didn't feel you needed to spend time there in the morning you could leave Verona early and stop in Sirmione for a couple hours before it gets too crowded and then head north. I stayed in Malcesine and loved it. I personally wouldn't bother with staying in two locations. You can take the boat around the northern section and if you really want to see something in the middle area you do have a car.
When we were in the Dolomites we actually based the whole time in Bolzano and loved it. I know this is not what most people want but it worked for us. We enjoyed having a small city to some back to after driving/hiking day trips and I found the villages in the Ortesei region kind of boring. Usually I love small villages but in this case they just seemed like ski towns to me (we were there in July).
You will probably find some useful information in this trip report - https://www.fodors.com/community/europe/a-month-in-northern-italy-mountains-lakes-and-castles-1072263/
I visited the various places you are going on multiple different trips so no one trip report covers them all but there are photos of all those places here: -https://andiamo.zenfolio.com/f739967755
And this report covers Bologna, Parma, Modena and Ferrera - https://andiamo.zenfolio.com/blog/2019/10/bologna-and-emilia-romagna-july-2019