Try to get there early Monday or Sunday night. Nationals is pretty crazy and figuring out where to go and what to do can be daunting for a first timer. If you have all of Monday to check in, get teched and walk the course it will go a lot smoother.
If you do get there for Monday Kim and I host a lunch every year (this will be the 7th year) so you should come to that. Last year we had between 100-150 people show up.