Have a good browse of the VD Motorcycle Touring & Tours forum, especially look at some of the stickys- you will find lots of GREAT general info there.
For your trip, you are looking at an AVERAGE of 210 miles per day - are you up to that?? IF not, you either have to re-think, or had better start getting in some practice 'in the saddle'!
I'd be wary of changing your bike just before you go. Considering your current level of experience, you might be better off sticking with a bike that you are familiar with, rather than finding you have picked out 'something wierd'!! - HOWEVER, finally it IS up to you what you want to do, and I can't deny that a VStrom would be a good option, especially for a tall fellow.
IF you do decide to go for a new bike, be aware of the documentation that you HAVE to take abroad with you, including V5, MOT, Insurance cert - these are LEGAL requirements, so make sure that you get any new purchases done in good time to have the docs at your disposal.
After 12 days of touring, your confidence level will be increasing rapidly, riding in France et al is just much better than the beaurocracy ridden UK these days - definitely go for it, as you will be feeling much more natural on the bike on your return.
Finally, DON't get all 'macho' and let your mate push you too far out of your comfort zone (a bit out of the CZ is good but) - that is where danger could lie!!
