I second what chessnut said - Start paperwork now!
It took me 7 months to get all the information hubby and I needed for our application - and even after that we thought we had everything and ended up finding things we missed as we were getting ready to put it in an envelope to send. Which delayed us almost 3 more months. Our application was intended to be sent out in November and we got out in February *sigh*
You can end up having trouble at the border. I didn't get in "easy" I was honest, I just didn't give out unnecessary information. I mentioned nothing about staying longer, just said I was visiting with my boyfriend and his family (didn't say he was my fiance) she still kept asking when I was leaving and I told her my parents were buying my return ticket home so I didn't have a specific date (My parents were going to buy me a plane ticket, if I ended up wanting to leave or couldn't get my extension of say) I'm not saying to LIE please don't do that, you'll end up in pretty crappy waters. Just don't go up to the border patrol and spill the beans on your plan to get married. . .ect ect.