The best option is to stay at home till a couple days before your assignment starts. If you haven't maintained a home and have a couple weeks to burn, take your time traveling and enjoy the country. Sometimes the new agency will allow a few extra days if you have no place to go between.
As for negotiating salary, by all means, do. Agencies make a LOT of money off you. If you are skilled and a good fit for them, they will often negotiate, especially if you are a RN. If you don't need their benefits, you can almost always get an extra dollar or two per hour. Good luck!