I can help you out:
1- If the camera starts inside the van, then it's more accurate to say INT. VAN - DAY. If the camera starts in the van and quickly moves outside, then it's INT/EXT. VAN - DAY (NOTE: The latter is very rare, you're better off with the first).
2-The writers who put down A, B and C usually direct the scripts as well. They are basically structuring it as a shooting script, inwhich they can mark down letters, or numbers, for every scene they shoot (i.e. scene F, or scene 6).
3-You write MONTAGE: and then use -- for every time something happens (e.g.-
MONTAGE:
--They get on their bikes
--They speed down the highway
--They pass by a couple mountains.
--They arrive at the agency.
BACK TO SCENE).
4-You can do this in one of two ways. I reccomend the above aforementioned, but you could literally do a seperate scene heading for every one-second shot. I think that's a pain in the ass, but that's just me.
Sidenote-The best books to read before you, as you, or, in my case, after you've write your script:
SREEENWRITER'S BIBLE - David Trottier
HOW NOT TO WRITE A SCRIPT - Denny Martin Flinn
ADVENTURES IN THE SCREEN TRADE - William Goldman
STORY - Robert McKee
Best of luck.
