How many branches should I trim off the plants?

you don't need to cut off anything - might want to consider topping them before going to 12/12 though.

If I top them I'll lose the top cola, and in its stead I'll get a couple smaller ones...right?

I use the FIM technique and top once. I usually end up with 4 extra sprouts on top - here's a pic a few days before switching to 12/12 (about a month old i think with a 12" ruler for scale)

Can you post a link to a diagram showing the FIM tech. It sounds good so far.

Here are a couple of links and some pics of the above plant before/after topping...
Fimming and Topping 101
How to Top Plants?

So it looks like there is some conflicting info as to when I should perform the topping. It's my plan to flip these to 12/12 on wed. If I top them all tonight should I wait longer than wed?

oh yeah - if you plan on starting flowering on Wednesday, then i'd wait for the next batch to top. After topping you should wait to switch to 12/12 until the new nodes (usually 2 - 4) establish themselves (like a week or two).

I guess it depends on why you're switching to 12/12. If you have to due to size constraints or you want a faster turn-around time - then you gotta do what you gotta do.

How many plants do you have??