23 1/4" according to the IRC 2003 code.
From the 2003 International Residential Code: 311.5.6 Handrails. Handrails shall be provided on at least one side of each continuous run of treads or flight with four or more risers. - Maximum riser...
Approx. 24".
yes
The observation deck is 520 feet above the ground level.
Wooden
Strategic Deck Footings Tips
Cleaning and Protecting Your Deck
How to Protect Your Deck
How to Choose a Deck Protectant