Yes you can. It will help if before you pour into the form you use a weed sprayer full of diesel fuel. This will help the concrete not to stick.
Not marine grade.
yes,depending on the size of your cabana it should be just fine but i would try and make sure you have some help placing the material up on the roof as 23/32's plywood can be quite heavy.
depending on the climate and where the cement floor is located yes.most of the time .but any wood under constant wet conditions on top of cement will decay.
i am sure you can order it but if not you can always order your 2 full sheets online purchase and pick up at you closest store.then while at will call (where your item is held)you can ask the associate to have them cut to your specification's.
treated with aldehydes in the glue to resist separating.yes treated to be buried in the ground and cement poured on it no.
Most home depots have a giant table saw in the back of the store where you can request that the wood be cut (for free). The only downside to this is that the blade is usually dull, so, the cut may look a bit ragged. Ask them when was the last time the blade was sharpened?
It does not seem to be FSC certified; since it is not stated in any of the writings on it. There are other plywood sheets available, that are FSC certified. For the same thickness it would cost approximately $11.00 more per sheet.
if you order for in store pick up yes. they will cut it in the store for you.
understanding children and beds.it could be done under the right conditions but i would highly recommend purchasing a bed from a qualified retailer. just in case.