Hey Nelson84, you have to leave the country every 3 months and have to be out of the country for at least 48 hours. Buuuuut, you can renew for another 3 months and extend it, if you go to an immigration office in any of the big cities. So that avoids the travel in and out of the country for you.
You should stay as much time as you feel you need to get a feel of it. I go down every couple of months for a week, but I can't stay out of work for so long, and New Orleans isn't as cold as Canada.