Front and rear

OK, you've decided to use panniers. The next choice is how many? For fully loaded touring, I think your best bet is 4. That way you can spread the load and have a bicycle that is easier to handle than one that has all of the weight in the rear. And - you can more easily isolate your clothing, tent, and sleeping bag from the odors of food and fuel. That's a pretty important consideration if you're traveling in bear country.

For credit card touring, you can probably get away with 2 panniers. My choice here is to use just the rear panniers. And in fact, I'd probably use my front panniers on the back because they are smaller. (If I felt I needed the space in my rear panniers, I'd probably be more likely to take my trailer.)

I did meet another cyclist on the road who was traveling fully loaded (camping, without carrying cooking gear) but with much less gear than I was using (I think I may need to take a lesson from him...) He had only two panniers, and he had them on a front low-rider rack. He said that he preferred the bike handling that way.

I can't verify the front only setup since I've never tried it myself. As with everything else here, the choice is yours!