you'll likely be one of the first that gets the correct procedure. Dell should be contacting you once they have notice you've received the card.
Yes, they'll be sending someone to install it. Not sure how long it'll take to get them out there, guess you can let us all know hehe
as for the warranty, any dell product is covered under the warranty, installed by your or by dell. the "difference" is, if YOU mess up the laptop during the install, you sol. if Dell messes something up, like scratching Whackamacs case, then they are liable for that damage.
any installs have the possibilty of damaging the system. Heck, you could blow up a computer trying to change the ram if the stars aligned correctly

putting in the card is very easy, but if you are not comfortable with doing tech work yourself, leave it for them.