You're building a compression part. It doesn't much matter how you get the thickness, as long as it doesn't compress or delaminate. As others have stated, you can safely laminate sheets together if you just rough up the surface a bit and wipe it clean with a bit of acetone. Using thicker stock only makes your life harder and usually more expensive. Prices vary widely, but usually 1/2" is more than twice the cost of 1/4". Ironically, you can often find 1/4" for less than 1/8".
You don't need a special saw unless you're going to cut a bunch of it. It cuts pretty readily but won't do your blade any favors. Just use any fine-toothed blade you don't care much about.
About the only ways to go wrong here would be fail to roughen the surfaces before joining, to fail to clean the surface before joining, or to clamp the part too firmly and starve the joint. No need to clamp, actually. Just apply a generous layer of epoxy to both surfaces to help ensure you don't trap air bubbles. Then a little light pressure to squeeze out the excess is all that is needed. Let gravity do the rest.
Once you laminate your part and sand the edges even, go the extra mile and brush a couple of layers of epoxy on the entire part, especially the exposed edges. This is just cheap insurance against wicking and other water ingress that can occur. If the part isn't intended for submersion, this is overkill but why not? If you mean to paint the part, then this gives you a better surface to work with, too.
