So, where are you with it?

The part that gathers data from the sensors and the part that controls the fish feeder should be the same, but they can be quite separate (or not) from the part that interacts with the web. It may well be the harder part, too. If you build up a program that will do that then you'd have it half done. I'd be inclined to build that up as a class library that could be referenced either by a Windows app (for testing), as well as by an ASP.NET app for the web interaction.