Ok, so I'm generally new to mapping. I have an idea to create a map called surf_skifree except I need your help on what will be easy, hard, and impossible. I'm on a bad computer right now so I can't test out anything. An understanding of the game SkiFree will help you help me.
Here's a list of what I need to know:

Can you surf downhill?(not gliding on something to the left or right, but below + behind)

Or can/should you create a slightly slanted no friction surface that you can maneuver on with ease(able to move any direction, jump, and stop).

Can you create flags that turn into a smiley face once passed in the correct direction?

Can you create an abdominal snowman that chases down and eats all people?