For this sort of level of riding, just go out and enjoy yourself, get some miles in, sprint a bit now and again, take some hills in - above all enjoy it.

Fit riding in around the rest of your life, but do as much as you can.
By simply training you will quickly reach about 90% of your potential fitness level - this is pretty fit, 440 miles will be easy to you.

Then you can decide if you really, really like it enough to add the extra 10%. This last bit of uber-fitnes is HARD to gain. This is when getting scientific and really thinking about and planning what you do is important, as is organisation and dedication.

Its all a matter of deciding what you want out of the sport and what you want to put in - enjoy, don't worry!

Good luck in China. Please let us know what its like.