Other Item discount modifier Questions

Hello, I have a question regarding Promotion modiers using and Other item discount. We are working on a promotion in which if a customer purchases an item in certain price category, they will receive a discount on another predefined item (loaded into the "Define Details" field. Since the "other item" can only be loaded by item number, we will have to load potentially thousands of lines into that field. My question is, are there limits on how many lines can be populated in the define details field? Or will it hold whatever quantity we requre.

Secondly, is there a way to acheive this discount other than the way described above? Basically, we want to give a discount if Product A and Product B are ordered together on the same order, i.e. a conjunctive discount.