You may have to watch out because the GPLv3 is designed to prevent this sort of thing (having some GPL'd software inaccessible on the server side (the "application service provider" loophole)).
So it could be a problem, I'm not an expert on this.
if it is AGPL (notice the A), then you must provide source to to your users, whereas with GPL it's when you distribute the code (can't send precompiled webapp)
