I’m going to Misano in September as well. Hotels in the nearest town, Misano Adriatico, are almost already booked out! However they’re reasonably priced and within walking distance of the track and the beach! You can buy tickets online from ticketone.it, which has an online English translation. We’re taking the overnight ferry from Portsmouth to Le Havre, riding to Paris, then autotrain to Nice near the Italian border. Two weeks around northern Italy and back the way we came.
If going via the tunnel, you could go down through the Ardennes, the Black Forest and over the Alps?