Dee Dee,
OK, you have a lot of choices for finished print formats depending on whether or not you're going to print them yourself or have a lab do it. If you print yourself, you can always cut the image down to a more appropriate size.

I use MPIX as my lab (there are several really good ones out there but MPIX matches my files very well) and they have formats that range from letter size, 8X10 through square. Ultimately, you need to be able to crop the image to a format that focuses on the subject(s). If that's square, then make a square proof/print.

If you're cropping in PhotoShop, make sure you use the auto-cropping feature and it will automatically crop to the appropriate size at 300 dpi.

It's difficult to set up the shoot for any particular format. You fix that later in the cropping and print size. Never do weddings. Repeat after me: "I'll never do weddings". Thank you.

My format for most of what I do is letter or 8X10 but I can crop to whatever aspect ratio works for a particular image and still get a good print from my lab. Stop feeling limited by the capture aspect ratio (8X12; 4X6) and think instead of what format works best for the image you've captured.

Jim