I've never printed from home either. I think almost all of my prints were ordered from Nation's Photo Lab. If you order when they have a promotion going you can do quite well.

I need to research more about how many pixels are needed for what size. I see Imaging Resource for example says, "The Canon 6D prints superb images. Stunning 30 x 40s at ISO 50/100/200; an excellent 16 x 20 at ISO 1600; and a good 5 x 7 all the way to ISO 25,600.

There aren't enough pixels to do that without resizing/upres quite a lot. If you're starting file size is 5472x3648 and you want to print 30 x 40 then you'd have to first crop to 4864x3638 and only have 121 PPI. I highly doubt that would look good.

How would you make a 30 x 40 with a 20 MP camera and have it look good?

Dave