The glass was not that that heavy, As I recollect it was 3/16" thick. We sat on it, slept on it etc-never stood on it however. The teak fiddles kept the glass in place,--never had any question or issue of the glass coming out of place. I suspect that the glass is still on the table--current owner of C-Pelican?
Both polycarbonate (generic--Lexan is a trade mark for polycarbonate) and Acrylic (generic trade name is plexiglass) will scratch, and can be obtained in "scratch resistant coatings" We made large polycarbonate windows which overlaid the original window openings on the Cal 46 pilothouse--about 1/4" thick, was very impact resistant. It had the "Scratch Resistant Coating"--but if anything sharp/hard hit it, it could make a scratch. The windows were still optically clear after 40,000 miles and over 6 years when we sold the boat.
I have a "laminated" map on the current C Dory 22--and somehow some moisture got under the corner, and it is delaminating. So just having a laminated map or picture etc on the table, does not warrantee it will not have issues.
Most of the professionally built tables are a clear epoxy. We made several in the past, with photos embedded in them. That weight is about as much as the safety glass. Just any epoxy will not be satisfactory, there are several special formulations such as:
http://www.bestbartopepoxy.com/epoxy/ Look up the techniques about getting the "gas" bubbles out of the epoxy as it is poured. There are also acrylic casting resins. I think the Epoxy is better for table tops. If you start with plywood, you will want to be sure it is thick, and then put fiddles on the sides--teak are good--but any durable wood will work. It is going to be easier to get a good surface with a epoxy if there is a lip, and you don't have to deal with edges. You will have to finish the plywood, with some paint or surface which will be compatible with the resin. You might even consider some laminate surface. The epoxy should stick well, and it will be easier than trying to get a perfectly fair plywood, painted surface.