Need thoughts and advice: Prague to Vienna

I'm from the US and I am planning a short tour from Prague to Vienna roughly following the greenway, and possibly on to Bratislava, in August. I'm a cycle commuter – 6 to 8 hilly, hot miles (10-13 km) daily. I used to do solo touring, so this isn't my first rodeo, but this will be my first tour in decades. The plan is for 5-6 days riding, with one full day on each end enjoying the cities. I'm tentatively planning to rent a bike rather than bring my own.

A few questions:

1. General thoughts on the route and its difficulty?
2. Opinions on whether I should also rent panniers, or should I bring my own pre-packed?
3. The bike rental will come with platform pedals. Thoughts on whether I should bring my clip-ins?
4. I can also rent a helmet. It would save trying to get mine there intact, but I would prefer my own. Thoughts on that choice?
5. I've played with the idea of Berlin to Prague as an alternative. Easy, but looks a little boring. Thoughts?

Thanks in advance!