Holland / Netherlands

I'm planning a week's tour of Holland in June. I'm taking my wife who is a novice to cycle touring. The plan is to take the Newcastle-Ijmuiden ferry and do a 5 day tour returning to the ferry, covering about 50 miles per day. I've been to Holland before but never cycle touring. Some good advice on this thread already but I'd welcome any advice on:

1. Where to go. Where are the 'must see' places in Holland?
   
2. Is it best to pre-book or just wing it? Are there any good websites for cycle-friendly accommodation?
   
3. Where to get information on long distance cycle routes in Holland.
   
   

Many thanks.