Mappage can be a problem on long rides. You can buy detailled maps along the way and use a small scale map for general guidance. Ordnance Survey maps are widely available even from village shops.
The CTC will have some info on routes.
Traditionally the routes is ridden from Cornwall to Scotland because of the generally SW prevailling wind.
If you are not camping you can go fairly lightweight. Try a few weekend rides to sort your essential luggage from nice-to-have. I find that 2 small panniers and a bar bag work well.