We all start somewhere. How do I?

Greetings, Unity people!

I am new to this engine called Unity. I'm trying to make a 2D flying game like Gradius III (SNES). (YouTube Let's Play - action starts at 9:08) I'm trying to follow the Unity 2D tutorial. The 2D tutorial was intended for Unity 2.x, but I'm on Unity 3.5.3. Maybe it's a version discrepancy, but I found some oddities about the sample game:

1: If something leaves the game bounds, collision goes crazy! Try knocking a crate into the death zone. You'll see.

2: When in the spaceship, I fly directly up and see a crate on a platform which I can't reach because the ship's collision goes crazy! (This is probably related to 1.)

3: If the sample game freezes or crashes, I need to force close the Unity editor too. Is this normal?

Sample Scripts

Regarding the sample scripts, I don't see the Start() function in MonoDevelop that the tutorial references. (There's a Start() in two other places.)

Combining Children
What's the best way to combine children if they aren't the same object? For example, a flat platform and a sloping platform.

Ensuring 2DNess

How do I set the Z position of everything to 0 at every frame or every update?

For Much Later

I want to add player customization, so they can use their own avatar/ship instead of a stock ship. How does this work?

Otherwise

I'll continue with the tutorial. Any better samples out there for what I hope to do?

Board Stuff
When I edit a post, why do my < BR > tags break? They turn into < BR /> tags with an empty line above them.