I also have given up sleeping on the ground. I don't even carry camping and cooking gear (saves 10 pounds, at least) anymore.
On my first bike tour, from SF to LA, I did 70 mile days. This was too much and I have since tried to cap my days at 50 miles. I've also learned to limit my routes to 4000 feet of climbing per day. When in doubt, I select shorter days over longer days. I also try to schedule a rest day every 4 riding days. Of course, these are flexible limits, but experience has taught me to respect them.
I also add extra days to the schedule for emergencies, such as bad weather (I try not to ride in thunderstorms), mechanical problems, or the desire to spend an extra night at an interesting place. For a 12 riding day tour, I'd plan 2 rest days and add a day on the end, or a trip of 14 days: 11 riding, 2 to rest, and 1 just in case. Riding 20 miles when exhausted sucks the joy out of any bike ride.
As for places to stay, I'd strongly urge you to join warmshowers.org, a site for matching touring cyclists to overnight hosts. This is a free service all around and meeting other cyclists is always a trip highlight. While sleeping in a hotel is acceptable, it is much more pleasant to sit around and share stories and experiences with people I share a passion with.
As mev said above, often there is no reason to book in advance unless you will be in a place with limited options or during the high season. I am a compulsive planner and often have hotels booked weeks in advance. But, I always choose places that can be canceled without penalty as close to the date as possible. If you are booking at a non-chain motel, it is often a good idea to call them, explain that you are a traveling by bicycle and your schedule isn't set. Often, they will extend their cancellation policies to meet my needs. I always contact these places when I am certain I will be able to get there on the appointed date.
I wrote an article about
how I plan my (credit card) tours, which you might find informative.