Cycling

I used to cycle everywhere; to school, to Guides, to go riding - it was how I got about. However, I haven't really done any cycling for years. This was because when I lived in Guildford there were hills and also the roads are awful with potholes and drivers passing very close. However, there is a challenge to be met - to cycle from Guildford to Shoreham along a former railway line - so no hills. I am wondering whether I should start training now - and then go and buy a bike (because the training will be in the Gym). What do you think?