Cyclists Touring Club
: it's worth going for rides with your local club for some advice and training.
Lands End to John O'Groats: the CTC have routemaps for the journey based on aover 100yrs experience.
A touring bike is probably the best style for a long tour on roads when carrying luggage. You can tackle most tracks and trails and I have used one on extreme mountain trails.
Lighter weight touring bikes, called Audax are better suited to faster long rides with light luggage (eg supported by a van or hostel/B&B style).
The standard road bike has no luggage capacity , limited tyre clearance and often high gears so I wouldn't recomend one for a beginner.
You can get entry-level touring bikes from Edinburgh Cycles, Dawes, Ridgeback and Saracen.
Used touring bikes are not cheap but fo hold their value well. The CTC is a good place to buy used.