The M1956 suspenders would be totally incompatible with Dutch army equipment at any time (although they would work with Korps Mariniers equipment). The army equipment was based on British WE 37, with the exception of the canteen and etool carrier, which hung on the bottom edge of the webbing belt using M1910 hooks. Note, however, that the belt had eyelets only on the lower edge, so it would be impossible to attach the M1956 suspenders (no eyelets on the top edge). One of my other posts shows a complete set up of army equipment (M1952): https://iacmc.forumotion.com/t10459-dutch-web-gear
(see post #13-14).
Korps Mariniers webbing was based more or less on US M1910, so the suspenders would have worked with that stuff. Also, green leggings are typical of Korps Mariniers items. This would also explain the cartridge belt, as it would be compatible with the M1910 and USMC-type gear that the KMarns used in the postwar period. It is not unusual to find US items mixed in with KMarns equipment of Dutch manufacture. Does the ten-pocket belt actually fit carbine magazines? If so, it must be a little bit oversized.
So as far as your Dutch stuff goes, you might have a mixture of army and KMarns items.
The Belgian magazine belts come in at least three different types: one is like yours, one has six magazine pockets, and one has a mixture of FAL magazine pockets and one or two smaller pockets. I have all three types, but have no photos to post at the moment. I believe these were intended for soldiers armed with the heavy-barreled FAL.
Strictly speaking, these belts are not based on the M1937 BAR belt (which used a much narrower buckle), but rather, the M1918 pattern, which had the very wide buckle. You will not likely see M1918 belts still in front-line service by the Second World War, unless they were retrofitted with the narrower buckles, as was often the case. Why the Belgians opted for the old wide buckles, which are very uncomfortable, is a mystery. These belts are sometimes seen with fake markings to give the impression that they are British-made BAR belts.
The holster remains a mystery - it is nothing like any of the standard Dutch or Belgian holsters that I have seen.