first, welcome aboard
second, read thru links 14, 15, 18, 2, 3, 4a and 4b in the DIY stickies at the top of the forum in that order. look at every video, picture and link. that will answer every question you can think of and many you cant think of
remember, your boat is 50 years old and has at least had 3-4 prior owners....... recreational boats are built to last about 15 years and be replaced. your boat lasted at least 3X its intended design life. depending on the year and manufacturer, your boat may be cored, it may be hand-laid, or it may be chopper gun construction.....
now on to your questions you posted
1 - no advantage what-soever, plenty of disadvantages. to get any strength, you need to be into heavy plate vs sheet, so you are adding hundreds of pounds of weight, where those two layers of 3/4" plywood covered with a few layers of 1708 and polly lasted over 50 years with shoddy workmanship. how do you plan on attaching the steel? assume you use a 1/4" sheet of steel. you still have to add 1-1/4" of wood to the core to get a total thickness of 2.00 - 2.25" so now you are out $300 for a full sheet of A36 which will start to rust right away. then the rust will migrate between the resin and steel and the bond fails. not to mention, short of having access to a laser, cutting and handling it would be a biotch. what prompted your thoughts on adding a sheet of steel?
2 - wood is preferred for the stringers and the deck. again, back to the steel deck you mentioned. you will be into 7 gauge at a minimum to prevent oil canning when walking on it. so for a 15 foot boat, assume 820# of steel to make a deck. what advantage are you adding to the boat vs the typical 100# of plywood and 2 layers of 1708. then you have to figure out how to tie the steel plate back into the boat hull and stringers to make that mechanical connection, where tabbing already does this. then you have the cost and the handling. how are you going to keep the metal from rusting? if you migrate over to stainless, your cost jumps up to 3x. you could jump to aluminum, the cost would be the same, however you would be closer to 320# (you have to jump up in thickness to get the same stiffness) this would most likely exceed the weight capacity of your boat.
3 - 3/4" exterior grade plywood is the most cost efficient, easy to work with and best for the job short of an engineered stringer tub which requires a pile of molds and a plexus mix gun to glue it all together
4 - yes she is, and if you are trying to re-invent the boat which will add thousands of dollars to the boat as well as thousands of hours of your time, she will probably shoot you.
now, what advantage would you have to add steel to the transom and deck?
