A BIG trip in 2023 sounds awesome, make up for all that we have missed over the last year and a half, right?
How long will this trip be total??
To ensure you have Calcio Storico as a possibility, first step is to make your vacation in Florence (or in Tuscany) fall on or around June 24th. The final is always played on that day (pandemics aside, of course!).
The hard part will be tickets -- often they go on sale the during the week before, and you can only buy them in person so the way to make sure you do get tickets is to be here the week before. So I'd say be in Tuscany from the 16th/17th or so and up to the 24th. You can divide time between seeing other parts of Tuscany with being in Florence, not just on the 24th of June.
I hope this helps at least in setting up some of your travel plans. Keep in touch as time goes by so that we can see how the game and sale of tickets goes in 2022.
As far as dressing up, most local fans dress in their team color and paint their faces in that color as well. The sections for the teams become that color. While the players have a sort of costume, they really play in a t-shirt or shirtless.... so as far as appropriate gear, considering it is June and warm, I don't think you want to overthink it or get overdressed. Only the people in the historical parade get dressed up in Renaissance period costumes.