Hahaha. This thread is full of forum cliche...
No. 1 package will not provide the proper pitching rate for 5g of lager beer. You will need 2 packets. Check here
for some good calculations for the future.
That yeast works very nicely and is the same strain as 2124 offered by Wyeast. I used it in my Oktoberfest this year to great effect.
Second, you should definitely rehydrate the yeast per the instructions. The only acceptable time to not rehydrate is if you are pitching warm (70ºF) which I highly recommend against.
I suggest you cool your wort to 5 degrees below your fermentation temp (~46ºF), rehydrate your yeast, and pitch. Then allow the beer to warm to your fermentation temp (~53ºF).
I did not rehydrate and had a very long lag phase as a result that I was not happy about. I also needed to do a diacytl rest after about 9 days when 3/4 of the fermentables were eaten.
KellyK had good advice. Buy Noonan's book. It is the best brewing book I have read. However, do not make a starter for dry yeast. Everything I have ever read recommends against it, and it is way easier just to buy a second pack.