I had a last minute order for 150 cupcakes for tomorrow...white with white icing. This is the first time I've done that quantity, so any tips for frosting would be appreciated. It doesn't have to be fancy, as they are making an arrangement out of the cupcakes themselves.

Also, any tips on getting the cupcakes to stay upright and nice looking for pick up?

Thanks!

Put them all in the boxes unfrosted, then pipe the swirls on.

Use a large tip, like 2D. Just swirl it around the cupcake and it will look like a rose. Very easy, very quick.
I also put mini marshmallows between the cupcakes so they don't slide into each other.

If you pipe the icing on, be prepared to make tons more icing than you think you'll need. That method uses a lot of icing. Also, consider the time you'll need to refill the icing bag or bags. That will slow you down.
And, do you have room for 150 iced cupcakes in your kitchen? They take up acres of counter space.
If you have to deliver them, do you have room in your car for them?
Can you get someone to help you frost and pack them?

Those are issues I faced when I made 300+ cupcakes.

Thanks! What other tips could I use besides 2D (I don't think I have that one)? I was thinking about the amount of frosting it takes--any other options for frosting besides swirling it on?

I use 1M. You can do it like giant stars if you're trying to use less icing. The swirls look more professional though. If you make the swirl a bit smaller than you'd think, so you can still see cupcake all the way around, it only takes about half as much icing and it doesn't make it topheavy, but still looks good.

I would do as TexasRose says, 1M - show some of the cupcake - that would be the easiest and the most professional looking.