When I left my job for Grad school (9 years ago), I made the mistake of telling them the moment I got accepted, which was about 3 months before I wanted to quit. Fortunately, I had a nice boss who really liked me, so I served out the rest of me tenure; however it did make things awkward for me to be there for so long when they knew I was leaving. My replacement started two months before I left, which was weird. I definitely felt extraneous.
When I got to grad school, I heard stories of other grad students who weren't so lucky. They told their boss and ended up being "let go" within a week of telling them.
If I had it to do over again, I probably would have waited to tell them until two weeks before I planned on leaving. You might check your employee handbook to see what sort of notice is customary. Many places ask for two weeks notice, but certain jobs ask for more.
You can certainly ask to have your vacation rescheduled ASAP, but I do not think you are under any obligation to tell them what you plan on doing for those two weeks. If your relationship with your boss and/or co-workers is such that you feel comfortable divulging that info, you can, but you do not have to. I wouldn't if I were you.