First time Applying for TN..HELP!!!

I am a Canadian citizen, received my education, and license as a RN in the USA, now have a position offered in the USA and need to apply for a TN visa. With all the extra security should I purchase the USA work visa kits online with sample letters, questions etc? What kind of questions do they ask? The hospital gave me a letter of employment without any time lines,, will this work? Any additional information would be greatly appreciated.