Do I need a whole new front assembly or just a new screen?

I suggest you replace the entire display assembly with a new one from Ifixit; part IF137-008-1. It is quick and pretty easy to replace. Just replacing the screen and digitizer is doable but very difficult and time consuming. If you want the phone back in operation quickly replacing the display assembly is the way to do it.

Please note that I'm not yet an experienced small device repair technician. What you read above is just my opinion. I'm basing it on attempting to replace the screen and digitizer of an iPhone 3G for a friend with parts from a different source, and failing. Then I ordered the display assembly and that worked out great. The friend is happily iPhoning. It was gratifying to see it all work so fast. --Bob