The PPI setting is in question. What you need to determine is if you have enough pixels in the image for the size that you want printed. For example, if you want an 8 x 10" print at 300 PPI, the math works like this:
10 (inches) X 300 (PPI) = 3000 pixels
8 " X 300 " = 2400 pixels
So if you want an 8 x 10" print at 300 PPI it would have to be 2400 x 3000 pixels. The PPI setting doesn't matter. The PPI setting isn't going to change the number of pixels. It's a number that software programs like Photoshop can use to display the size of the image at a given resolution setting.
You can wrestle with PPI settings all you want. And it isn't going to make any difference in the quality of the printed images. A lot of the book publishers today will warn you if there aren't enough pixels for the given size that you choose for the page. Good quality printing services can create large prints from smaller images. At least that is what I have found. But again, simply changing the resolution setting will have no impact on the quality of your prints.
If you want to test what I have told you, I suggest that you export an image with a setting of 300 PPI and then change the setting to 72 PPI and export it again. Don't resize the image. Export it at its original size. Send both images to Costco and have 8 x 10" prints made. Yes, it will cost you $2 or so, but you will find that there will literally be no difference in the quality of the two images.
So, technically for that, I'd only need 7.2 megapixels correct? So even if I crop an image way down I can print it out and it look good? Considering I have 36 megapixels.
I read your apply again, and yes, you have the concept.