Looking good so far - a few more planks - seat the tacks and blast-off!
As far as installations to the interior - putting your thwarts in place (or I usually use temporary thwarts - 3/4" scrap stock) Will help the boat maintain it's shape during the canvassing and filling. You may want to do your varnishing prior to canvassing - especially if the planks have some gaps. It will keep varnish from seeping down into the canvas and filler which might cause problems with the filler and paint. At the very least, it will keep the varnish from gluing the canvas to the hull, which could cause problems for future restorers.
Most of the 18' boats had 3 thwarts.
BTW, I get through the Buffalo area on occasion - be glad to stop in sometime. Great to see someone working on a boat with kids!