Plywood works fine as a shield material, though a max-size shield will be heavy. You don't have to coat the whole thing in foam, but you do have to have at least 5/8" padding along the edges. If you're using pipe foam around the edge of plywood, I like putting some flexible PVC tubing (the clear stuff) around the edge of the shield before attaching the foam. Otherwise the edges can eventually tear up the foam and you'll have to replace it.
Latex weapons are completely legal (on a case-by-case basis, as with all weapons), though they can be difficult to make. There are a bunch of tutorials if you go looking around online. The most basic core material is PVC pipe, though a lot of people prefer fiberglass tubes. You can buy those from
Goodwinds. I've heard there's a company that's a little cheaper but I don't know the name. Those aren't your only core options, but I'd say they're probably the most common ones.
In general, big pointed edges on weapons will make them less likely to pass, but if you're careful to build it in such a way that it's not going to hook anybody's weapons or limbs and won't stab anyone in the eye they're not outright banned or anything. There's sort of a common sense criterion there.
Shaped foam won't get you full armor points and it may or may not actually stand up to the physical demands of the game. If you can get it, leather or metal armor will work a lot better. I'm gonna second the suggestion of a Wisby-style coat of plates, it's probably the easiest style of plate armor you can make. I haven't made one personally, but it's on a looooong list of crafts I intend to eventually get to. I'd personally go with sheet metal over the barrel plastic they suggest in that tutorial, though.
