The width should be wide enough so that when you are playing on only one string the bow won't produce noise from adjacent strings.

The width should also be narrow enough so that, when you are playing on two strings at the same time, you can use one finger to press on both these two strings without much difficulty.

Suggested horizontal distance between adjacent strings is 9-12mm. Adjust it based on your finger width. You can also use your old bridge as a guide for where to make marks if you please.