Hi. Yes, logistics are quite easy once there; certainly if you have a car. I drove over from Bavaria the 3 years I did it, and stayed at Hotel Seelend outside town (Waitzendorf); even that was only about 15 mins by car. Loads of free parking there, and easy to get out on the bike for a shakedown from the hotel. Lots of parking at race too, as Matt says. They have changed the transition locations and run course slightly from 10 years ago, but essentially the event remains the same. Despite the hills, there are very fast flat stretches, and the roads are smooth. Biking was my weakest discipline, and I still averaged over 34kph iirc (best split was 2:33 I think). I didn’t recce the course, despite having a car, but it’s worth making sure your descending skills are honed! The descent after the first climb is fast and winding, and I have seen ambulances attending crashes! Make sure your brakes are sorted.
If you plan to drive there from Wachau, I would just consider what road closures will be in place on the morning, as this was a closed course in our day, assume so for Challenge too. I guess you could use the B33 & B1; bit of a drive though.