Check and you might turn up a comparison chart, or at least reviews of many of the cameras out there.

Most 4x5" cameras not specifically designed for wideangle use are either "double extension"--around 12"--or "triple extension"--on the order of 17.5-20".

You probably want a triple extension camera, since that will let you use a longer lens for this kind of work, which will give you a little more working space, so that the camera doesn't block the light and you get a somewhat more neutral perspective. You might also look for a camera that gives you the option of rear focusing, since that's easier to use for macro. The alternative is to use something like the Linhof macro focusing rail, which usually runs around $150 used.

If you decide you need more bellows, you can also use things like extension bellows and extended lensboards for closer focus.