How to format images to print 24 x 36?

I'm trying to take a picture (taken with Nikon D5100, in JPEG fine), and print it at 24 x 36. I want it to be at least 3000px along the longest side. Have 8- or 16-bit color, be in RGB with the color profile embedded in the image? And I would also like to know how to alter the proportions of the image.

Since the large image size is 4928x3264 pixels and the D5100 is in the 3:2 image ratio - the same as 24x36 - just take a picture and you are ready to get a print. The resolution might seem too low, but when you consider that a print this big will be viewed from a distance, it will be fine.