As somebody said before, Animal Speak is really nice. Although if you'll like the game, it will be much more important in OS2.
There's a lot of hidden stuff, try exploring as much as possible. You can also throw piramids (or teleport them) into various places to gain access.
Try to always have...
I dunno. 10-15? Not that much, especially that you can turn on insta-win in battles (recommended). If I remember correctly, to do this you had to go to the secret room in the bottom left of the basement - just "enter" the wall there