It's not a dumb question at all. You want at least 2 panels on each side. You may only need to actually use one on each side to cover the window (that's what I do with my grommet drapes) but when they're open, you don't want the stack on each side to look skimpy. Using two panels will give the fullness that a window that size needs.

I'm dittoing lukkiirish -- IMO windows look better with at least 2x window width in panels. So for example with your 66" window, at least 132" of fabric. So for 50" panels, I would go two on each side. This lets there still be gather when your panels are closed.

When you don't oversize them, then you have straight/taut panels when they're closed and it looks like... you didn't buy enough panels. :)

I have curtains all over my house where I have two panels on each side that are not sewn together. I think ideally they would be sewn together for opening and closing purposes, but they look just fine.

If you can't sew, you can pin them together with straight pins, just to keep them from getting a gap between them. The seams should not be too noticeable, depending on the type of fabric.

Thanks to all for your replies. Now I feel more confident to look online at curtains.

I haven't yet addressed the gap between my panels, and it's only been about 10 months since I put them up... o.O

(Ever notice how some things you KNOW you need to address, you still become blind to until someone else reminds you? :) )