Congrats on the upcoming purchase! As for the long trip:
* I fully agree with allocating lots of extra time and not being in a rush.
* In addition to plugshare.com and any superchargers, check out recargo.com (same company, one bought the other, and there's still slightly different data).
* Join the charging networks ahead of time -- SemaCharge, ChargePoint, maybe Blink, there might be others as well. (Blink is apparently having financial troubles. I haven't joined them yet.)
* And all of the above services have iPhone (and presumably Android) apps -- quite valuable on the road.
* Keep in mind you can charge at many campgrounds, you can search on sites like koa.com. Just ask in advance if they have "50 amp service" and if they'll let you charge your EV for a few hours (or however long).
* Also keep in mind many campgrounds are closed for the winter.
* Relatively few hotels advertise outdoor outlets or EV charging capability, but some do make them available to guests. Ask in advance, don't just pull up and plug in unless it's clearly a charging station for EVs.
* Last but not least, check out
http://evtripper.com/planner/carview_beta/ -- it takes into account speed, Model S battery size, passenger/cargo weight, elevation, wind speed (!), and of course distance, when estimating energy usage.
I just drove ~500 miles round-trip from DC to Pittsburgh and back, and I'm about to do it again. At the moment there are very few options for charging in between, but I made it with no problem. Details here if you're interested:
http://www.teslamotorsclub.com/showthread.php/19487-DC-Pittsburgh-driving-charging-experience