Creating Oversized Vinyl Decal in Illustrator

Hi!

I'm creating a decal that will fill a 41' x 9.8' wall space. It will be at the very top of the wall (I estimate the ceilings to be around 20-25"). Obviously this goes beyond the maximum artboard size for Illustrator. Would you:

1. Create the artwork at size and just expand it past the artboard?
2. Create the artwork at a 25% or 50% scale.

3. Create the artwork at size in separate files.

Lastly, depending upon the chosen option, would you:

1. Create it in 150 DPI.
2. Create it in 300 DPI so that the printer has the option to scale down.
3. Create it in an even larger DPI.