Rehydration is a good kick start to what the yeast is going to be living in. Bum is correct in his statement about using malt liquid to get things off sorry for not being more specific about protocol
As you have stated rehydrate with water (sterile) once you visibly see active movement in your culture vessel then add a mild solution of prepared wort I would suggest around 1025 OG this will get your yeast into a healthy environment for though fermentation
I feel that the rip the satchel open and sprinkle option has its down side having stated that there is nothing incorrect with it but I am sure your little creatures will be happier the other way.
Manufactures of dehydrated yeast have invested a lot of research hours and money in to there products I buy 500 gram packets of yeast and all of them have instructions for rehydration on the packet
They dehydrate it so it is easy to use with very reliable constant results and minimal wild yeast count
Sorry must sign off now the wallas and boks have just started