You should really do a lot of Satie before your tackle Slominsky. On the other hand, you very much can do PDQ Bach first (or second, or third, or other, or not).
There is a material difference between "on the tongue" and "stick you tongue out" particularly if a later instruction requires the performer to bite. I have the urtext and sadly there is no indication of what interpretation should be followed. However, I book on the performance practices of Satie's music (translated into English by J.L. Borges, of all people) clearly indicates that it is supposed to be either one or the other.
Enjoy your Satie. Very much do not understimate the aesthetic purpose of this music. A smile if not a thing to underappreciate.