Cheap and easy way - four 1" holes with refrigerator strip magnets
As far as number and size of valves can depend on the valves you use. Some valves have very small ports and restrict flow, I recommend finding valves that are "full port" so they don't restrict flow as much. If you decide to put the elbows and pipe risers I would go with 1" as people say that length of pipe restricts flow more. Otherwise I prefer 3/4" with either 3 or 4 of them, I have never needed more than 2 but I don't cook hot and fast, yet. The 1" fittings make you drill a large hole in relatively thin metal and feels flimsy plus at that size the curvature of the barrel starts to show and my fittings don't fit flush.
XL Big Green Egg, Weber Performer Platinum, WSM 22.5"