I am the lead developer on a thick client web app (Java swing) which we're looking at recreating as a web app. We're part way through some initial work, have chosen a framework on the server and integrated with our previous backend code. We're just starting to get into the client side of things, looking at javascript frameworks etc. The previous system was pretty sensibly architected so the logic is already serverside. The challenge ahead of us is really about redeveloping the user interface rather than anything else.

What would be the list of things to consider in redeveloping the entire user interface for any application? I'm trying to get an idea of how large a task might still be ahead of me and the team.