I don't see any reason why, with your criteria, you couldn't do the France ride.
TBH London to Brighton is probably tougher, you'll not be riding up anything like Ditchling Beacon, or any of the 2 or 3 other climbs, when heading to France.
The distance you can cover on a bike is difficult to...
You'll not be out of your depth.
What bike are you riding, is it fit for purpose?
You've still got a few months of training, which is more than enough time.
You need to start off little and often.
Don't over do it Sunday morning keeping you off the bike for a week.
Build up gradually, try and...