1 A retired Regular officer who also is employed by the federal government and is subject to the dual compensation statutes may have that reduction reduced because of the waiver of retired pay to receive VA benefits.
If they don't, then 4 thick is usually standard for a patio slab, how large or small it is doesn't really matter. The most important part is the sub-base. Make sure you have a good gravel base. I would recommend at least 12 inches of compacted gravel. I like gravel where the aggregate (rocks) are no larger than 1.
Any concrete deeper than 4 inches (101.6 mm) is well within the range of your capabilities, but increasing depth adds to the difficulty of the work. This article explains how to cut concrete for sidewalks, patios, basement walls and house slabs that are not normally deeper than 6 inches (152.4 mm).