Welcome to the world of H14 !
The hole at the bottom of the mast is for the mast step link. You don't want the mast to stay fixed, but rather rotate as to give the sail a nice wing profile; so forget about tieing it down.
For your second issue, download the "HobieU.pdf" document (really good stuff
) on the following page:
Although it will also show info for other Hobies, it will explain what position is best for which course and give you a reference document for other issues.
Good luck & have a great Hobie day !