I have done this job, many times and your need to think the job through as it can become a bigger job than may first appear.
When you remove the gunwales and ply wood from the deckbeams you may find that the beams and carlins become loose from the boat, these will have to be bonded again.
Next the tabernacle may also need replacing or rebonding to the hull again.
Replace any split or damaged woodwork while you have the plywood off the boat.
Have a look and put right any hull damage on the inside of the tanks if you have a full bulkhead or reseal the half tank tops to the hull again to help keep the tank water tight.
Paint or re flowcoat( colour resin mix ) the area in the tanks or above the half tank.
Improove the bow block that the forstay fitting screws into before you re deck with ply.
I put a coat of glueing epoxy on the rear side of the new plywood sheet when i get it. Let it dry hard and then cut the sheet to the sizes needed to deck the boat.
I then glue the deck down with an epoxy coat ( this time with coating hardener)all over the panel and an epoxy/thickening powder on the beams.
You can redeck a Wayfarer with two sheets of ply, one will cover the fordeck and forward part of the sidedeck and the aft part comes from the leftover part of the other sheet.
If doing a wooden boat with a ply top aft tank, you can still do it with two sheets, Well I Can!!!!!!!!
With the coating hardener you get a varnish type finish under the deck that is better for water resistance than the glueing hardener type. This will need less covering coats than the other type.
The new gunwales can go on in one or with a thinner lightwood strip first before the hardwood outer gunwale.
Shape, sand and finish with an epoxy coat or I used to start with a thinned 2pot varnish as it soaked into the ply and wood well before the varnish of your choice.
Epoxy finish on the new ply is great, but if you do it in anything other than the perfect and dry place you maybe unlucky and get a damp haze in it and your never get it out again. I never took the chance!!!
This may nelp you think about doing the job yourself, or not. It was one of my favourite jobs to do on a Wayfarer!!