FATCHANCE - Nicely done.
Just a thought regarding your ratio suggestions:
Any choice of gear ratios that allows a whole number division ( or non prime numbers) between the # of teeth back and front will probably adversely affect the life of the chain. This is because through the power cycle the front sprocket will always be lugging on the same teeth in the rear sprocket.
Here's an example: Using the 16/48 configuration you mention, tooth #1 on the front sprocket will always be driving teeth #"s 1, 17 and 33 in the rear. Given the smaller # of teeth on the front sprocket the wear and tear on the rear will be magnified if at least one of the two sprockets does not have a "prime number" of teeth. Examples are 13 or 17 up front and 41, 43 and 47 in the back.
Hope this helps.