bit of a late response, but 3 weeks isn't really a necro yet, so here goes:
1)it's
MDF. it sucks up fluids like... actually I'll leave that out
no really, the 'open' sides (and Ideally any piece of an
MDF board) should be sealed somehow. and no, a few layers of acrylic paint won't do the job. Getting some epoxy glues (if you can get polyurethane glues, go for it - they're less viscous which would make your life a lot easier when sealing the sides of a gaming table, believe me! do go for an extra layer with PU glue though. PU is often used for layering glassfiber mats - and for that matter anything used to layer GF matting for car repairs will do this job just fine. if you can actually get some GF mat/tape to stick around those edges good for you - it'll make it a lot more chip-resistant!)
2) meh. if you're not much of a woodworker and don't plan on being such either I wouldn't worry with this too much. having said that I have an idea or two which wouldn't take all that much time/skill/cost to execute:
- get a dremel.
- lay the boards to be joined side by side, bottom up.
- dremel out a couple of **straight** channels across.
- get some metal tubing/rods/whatever with that same diameter as the dremel bit you used.
- glue them in on one end
-...
- profit!
you could also dremel room for some ND block magnets in the boards - my concern would be, however, that you'd have to glue them in rather carefully to prevent them from either tearing loose from the board on their own or worse, tearing little bits of the board off with them.
also the kind of magnets that would make a difference on such a project are both extremely scary in strength as well as in cost
...so maybe just don't.
3) ...oooh dear. that won't do. no, really. 8mm
MDF is not something which will even remotely support it's own weight in any way without warping the first time you look at it (or look away for that matter. it really does love some good old-fashioned warping!)
15-19mm-ish is pretty much the thinnest
MDF I'd use for something like this.
better still would be to use aforementioned 8mm
MDF but build a bracing frame under/around it.
now from your post I take it you have no interest in learning to work the tools to do that neatly but it's really not too much work.
if you're still interested,
PM me and I'll draw you a diagram or two