Currently it's not possible to add an OR Condition to a Rule. The Conditions are automatically AND linked. I had some cases where it would be great to add two Condition and link them OR. By the moment I do it by Custom Code.
This could quickly get complicated if you want to nest them. I would suggest at least as a first step to have a radio selection "flag" to let user decide whether ANY (OR) condition must be met, or ALL (AND), and you can do only one or the other.
