Different people have different preferences, I probably more different than most.
I was just thinking today of perhaps taking a trip into Tuscany in early April because I have never been there at that time of year, so it is interesting to find your post.
Personally I think you are shortchanging Venice quite a lot. I'm assuming (right or wrong?) that you will be arriving from home in Hawaii.... after a long flight, or probably in your case a couple of long flights, you may well be a zombie. If you have 3 nights in Venice, at the best of times you only have two full days of sightseeing. The best times to see Venice without too many people around is just after dawn and from late afternoon into the evening. The first day you will miss the morning (maybe more, depending on when you arrive), and the afternoon or more will be checking in and getting your bearings, while tired. The next day you will likely suffer more jetlag so may miss either the early or late part of the day, and as the evening approaches for your third night you will be contemplating moving on. I'm one of those folks who likes my Venice in week long chunks. I don't expect you stay for a week, especially on your first visit, but I might suggest 4 nights.
I also think that just one day of sightseeing in Bologna shortchanges that special place. Can you add one more night there? Do you want to make the shortish trip over to Ravenna for some of the incredible mosaics? If you get hooked on them at St Marks in Venice or at the incredible church on Torcello you may decide that a side-trip would be a good idea.
I think - only for myself - that 6 nights in Florence is more than I would want to spend.
Are you doing more than Italy on this trip?