What kind of plywood? I assume I should be using 3/4", right?
I keep reading about birch plywood & baltic birch, what's the
difference & which do I need? Or something else?


baltic birch comes in 5 foot square sheets. everything else comes in 4
by 8 foot sheets.

baltic birch has all of the layers made of birch. everything else will
have something else for the middle layers.

There's more difference to baltic birch than just that all the plies are
birch. Baltic birch is guaranteed to have no voids so you can show
exposed edges and not have to worry about a big defect which other
plywood may have. Otherwise, though, the outside layer in baltic birch
plywood have about zero character whereas birch veneer plywood can have
outstanding figure. If your going to varnish, I'd probably go with a
birch veneer plywood and plan to use some treatment of the edges such as
solid wood or banding. Unless you take a look at the routered edge of
some BB plywood and decide it's an effect you like.

bob g.