You'll definitely need to boil the wort after you mash, just to make sure it's sanitized. I think you could do a short boil though, say fifteen minutes. Also I wouldn't worry about adding any extra hops; think of it this way, you're not putting any hops in with the DME or dextrose, so why would you hop the extract from your mash?
To add to what RobertRGeorge was saying about time: I bought a 20 minute boil kit from midwest, and then decided to do a mini mash with some oats and two-row. it went from a two hour brew day to five hour brew day. It turned out great, though!