Long Distance Route for a Beginner!
A further suggestion: before your last training ride but after most of your training miles, get the bike looked over by an expert. This probably means booking it in to a shop for a service (clean it first) but it could mean instructions and/or an knowledgeable friend. This would also be a good time to get some tough tyres put on if they're in the budget.

Also (things that have caught me out on long day-rides etc.):


Carry tubes as well as patches  (which are a pain in the wet). 
Test your pump from flat before you go. 
Try out your clothing as well as your bike. 
Figure out your navigation. For example I like a smartphone in a cheap top tube bag, displaying a route prepared in comfort but not turn-by-turn directions. There's free software that uses openstreetmap (also free). Others take different approaches. If your distance is a challenge to start with, getting lost really saps your willpower. But of course you may want to explore along the way. 
Carry full finger gloves even if you don't think you need them; carry fingerless as well if you're prone to getting hot 
Get on the bike as much as possible before then. Even if it's just going to the shop the day after a long ride.