Hi Julia..

In terms of what you need to do physically to do what you want to do, here's my advice.
Do ride as much as possible prior to taking off. The big deal is getting your rear end used
to a saddle, which I recommend Brooks. www.brookssaddles.com

There are numerous books on getting in shape but the real secret is just take it easy the first 3 days.
Not more than 30 miles or about 70 kilometers a day regardless of how great you feel. From the 4th to thee 7th day increase you miles or kilometers up to 30% BUT listen to your body. Take breaks often
and take a day off to do personal things such as laundry etc. You should be fine after that and know what your comfort zone is. Regards, John Young