HOW MANY IS TOO MANY?

I know... I said I would never build another boat. Unfortunately, one boat will not fill all your boating needs. A kayak is great for navigating small water with physical effort. The 16 foot sailboat is good for bigger open water. But what about the in-between?

I want a boat that is quick to get on the water, and small enough to go down the small canal with bridges. But I want the option of a small sail for when I reach a small bay. Here is a list of requirements:

• Must be small and light enough to pull on dolly behind bicycle.
• Must have mast that will fold down.
• Sail must furl for quick adjustments and neat storage when folded down

I don't even pretend to be a boat designer. Everything I have made, I bought the plans. Here are some questions I have:

1. How narrow can you go and still be fairly stable with a sail, and without out-riggers?
2. Could I use a little balast with a more narrow boat to make more stable?
3. Is there a formula for length, width, sail area?

Duckworks was the first place I went to look at plans. What about the Rodent? Or the OZracer? 

If anyone has experience with these specs, or can point me in a direction for research, I welcome all suggestions. Like my friend always told me... you can never have too many boats.