Looks like I won't be going this year
As for tickets - we never bought ours in advance... the 2 years I've been, we've stayed in a B&B on the otherside of the lake (Portschach to be exact) and got a speedboat across the lake each morning to Maria Worth. When you got off the speedboat at Maria Worth, there were people waiting at the piers that you paid your admission too. Was something like €4 a day or something equally silly cheap!
As for the show itself, the best days to go are the first couple of days before the weekend. The locals turn up at the weekend to get drunk and there were quite a few instances of drunk people falling onto peoples cars the last time we went. Full or drunken idiots tbh...
If I remember rightly, we went over on a Tuesday and came back on the Friday last time - spent Weds & Fri at the show and Thurs just went for a drive about (& popped into Italy for a bit, as you do!

)