A: The min diameter on this clamp is 1-3/4"
A: As long as you have the proper barbed fittings for your hose these clamps will work fie. If you need barbed fittings Home Depot has them.
A: I see no reason why these SS clamps would not work to hold the fence matierial to the PVC framework. Without a doubt; the cost would be more than the the zip ties, and unless you plan a cover or top; I am not certain that the fencing alone would be much of a barrier to keep your cats in and out of the street.
A: I think this would be a preferable alternative. They do make UV-resistant zip ties but if you use these, you won't ever have to worry about replacing them ever.