I would always go with pants that are too big. You never know how much the manufacturer is going to leave in a seam allowance. Sometimes, there is just nothing there to let out.
You can alter the crotch/thigh area at the same time, basically. The waist is not difficult. You should use these directions if you need to split the waistband. Otherwise, use the directions for letting out the waistband here. Just make your seamline to the left of the original seam, not the right, as shown. If the pants are facing the way they are in Step Four, the left will take them in, the right will let them out.
I am currently working on a page for altering the thigh. It is on women's pants, but the instructions are the same. Let us know how things go.