A Full Monty is a fairly challenging ride and will need a combination of serious planning followed by excellent weather and cooperating traffic.
GB-only BBGs are fairly challenging and need a combination of excellent planning followed by excellent weather and cooperating traffic.
In your shoes I'd be spending a lot of time making sure that my routes and weather forecasting were as thorough as I could possibly make them and I'd then be getting a grownup to check my calculations.
Despite my opening bid, you're never too old so stop dithering and get on with it.