I only used the Trailblazer Walking Guide, I found that this was the easiest long distance to follow, even easier than the South West Coast Path where you only had to keep the sea on your right hand side! I did borrow the OS maps from the library in advance and copied bits of it into the Walking Guide e.g. compass bearing to various mountains. Looking at the Guide it suggests the Harvey strip maps at 1:40,000 although either side of the trail is limited although it extends to Ben Lomand, Ben Durain and Ben Nevis. It adds that if taking the OS Explorer 1:25,000 maps you would need six 348, 347, 364, 377, 384 and 392. If taking the Landranger 1:50,000 you would need four 64, 56, 50 and 41.
For the Great Glen Way I used the Cicerone Guide by Paddy Dillon. Again this trail was pretty easy to follow.
Live each day like it's your last. One day, you'll get it right!