Lots of hostels in Rome seem to have an upper age limit for the dorms, I don't know why.
The Rough Guide Italian-English phrase book is great for those of us who don't speak Italian. If you've got the time and cash, the Pimsleur language CDs and the Rosetta Stone language learning software are a good start towards speaking Italian. Any effort to learn Italian will pay off, even if the best you can do is "parla Inglese, per favore?".
Did you get to the Plano Grande?
I'm still up in the air about camping gear. Campgrounds are getting scarcer as land gets developed, and I didn't use my camping gear quite enough, but I had an awfully good time in the campgrounds that I stayed in. Definitely keep the camping gear as light as you can if you bring it.
There are one or two long distance high speed trains between Italy and Austria/Germany that are operated by Deutsche Bahn and by Österreichische Bundesbahn that will carry bicycles on the Italian portion of their routes. Otherwise, taking bicycles on a train in Italy is not easy. Even the slow regional trains don't always take bicycles, so if you miss one bicycle friendly train you could have a long wait for the next one. And yes, you will regret every extra ounce of gear you brought as you haul your loaded bike up and down stairs and into and out of trains. Ride your bike, not the train as much as possible.