Hi Joyce
From a legal point of view I think the answer is different than from a marketing point of view.
First of all, if a vendor does not explicitly restrict the number of other affiliate links on the same site/page, which most don't you are free to put as many on the page as you like.
From a marketing point of you you should ask yourself the question whether it really makes sense to have a bigger number of vendor links on the same page.
I think it really makes sense in comparisons as you deliver a value to your reader/customer and if you manage to let every product sound good for a different group of people your chances that they buy one of the products rise. There is no real rule how many products work best - there are too many factors to it.
I'd suggest splittesting until you know what works best...
Mike