You will enjoy it more if you plan it yourself, and you will not be alone; sometime there hundreds of people along the route flogging northwards or Southwards.
Doing your own planning allows you to be flexable, if you want a day rest then you can, if you feel that you want to push along and do 140 Kms then you can.
I know it sounds scary if you have not done any tour planning before, but when you get home afterwards you will feel more chuffed, than if you used a organised tour.
The many times I have cycled all or parts of the route, I have always been able to find YHA or B&B, but it pays to start looking a few hours before dark, incase you need to to try a few places.
On here alone there is so much knowledge availble, plenty of routes you can chop and mix to suit your needs.
Masses of information on this site:
http://www.cycle-endtoend.org.uk/