Is it ok to believe in many different pagan gods and goddesses?
If you mean, “Is it okay to be polytheistic,” yes, emphatically so. The world is, in my opinion, full of spirits.
My notion is that these spirits are limited in both time and space: they’re not omnipresent, omniscient, omnipotent, or any other omni-. They’re powerful, but not all-powerful. They’re present, but not always there. They’re wise, but not all-knowing. And this idea that they don’t know, control, and create everything actually helps deal with larger theological questions at least as well as (if not better than) monotheism does: after all, with polytheism, you don’t have to believe that one all-powerful being both created evil and consistently fails to destroy it (as one small example).
If you mean, is it okay to believe in gods and goddesses of various cultures at the same time, I think the answer to that is also a “yes.” Generally speaking, I think if you already believe in a bunch of spirits, it makes sense that you don’t (or any particular culture doesn’t) know them all: there are mysteries out there and strange beings presiding over things you’ve never heard of. Deities, also being limited in space and time (not all powerful or all present), can’t do everything, so other cultures would have their own deities.
Another point worth making: Paganism is less concerned with the details of how you believe or what you believe in than it is in what you do with that belief. If it makes you a better person to others, and improves your life, then whatever you believe is a positive part of what we, as a human experience, are participating in. And that’s beautiful.
Anyone who belittles your belief is really just a jerk.