Couple of us flew Manc to Venice- Marco Polo, we then stayed at Camping Rialto & could leave our bike boxes & bags in their left-luggage (for a fee), which was also a good base to mooch into Venice, as there's a bus stop at the entrance. If anyone stays here i would strongly recommend getting something with Air Con though.. It also has good bus access to Mestre, where there's lots of places to eat & drink, but not at Venice prices..
https://www.campingrialto.it/en/home-page-english/
If the start is in Cittadella again, it's rideable from the airport/Camping Rialto/Mestre area (Flatish~50-60km), or train from Mestre..
In Cittadella loads of us stayed at Hotel Filanda, they had secure bike storage & will take left-luggage.
https://www.hotelfilanda.it/en/
There's an ok bike shop in Cittadella, but a really good one at the foot of Monte Grappa called Moretti Basssno-
https://blog.morettibassano.com/
It's worth leaving a day or two spare to explore as there's plenty of places to visit. Aside from Venice, Padua & Bassano are supposed to be worth a look.
If looking for somewhere to eat in Venice & are yearning for some spice instead of more bread & pasta, Orient Experience Afghan restaurant was really good & reasonable $$..