400 cc should be any problem. most of the people reading this started doing long trip years ago on bike and scooter that were 125 to 350 cc . Eg honda dream . 2500 to 4 grand buys a used one .
Life's journey is not to arrive at the grave safely in a well preserved body,but rather to skid in sideways totally worn out shouting WHAT A RUSH, WHAT A RIDE.
"Life is a tragedy when seen in close-up, but a comedy in long-shot." Charlie Chaplin