I can set VIM (and most any other editor worth its salt) to "replace" a tab with a certain number of spaces.

I can't set ANY editor to logically replace 4 spaces with a tab.

When working on code with a group, it's best to default to spaces. This way tab-people can set their editors to replace with spaces, and space people can just do their thing. You CAN'T do that in the opposite direction.

As long as you're not screwing with the way C performs the action, I don't see why not. In other words: x++ and ++x are two completely different functions.

So, doing x *= ++i will perform:

x = x * (i + 1)

But, doing x *= i++ will act like:

x = (x * i) + 1

Beyond that, style is up to you. Most C-coders (and style guides) won't want whitespace around the variable, or between a variable and increment operator. But, if it's code just for you, who cares?