As Bill said this is an advanced kayak design. If you have other kayak experience go for it; other yost designs have a higher initial stability.

Skip the bandsaw. The best tool to cut out the cross section forms is a jigsaw. Using 3/4 ply will work with no issues. It doesn't have to be marine plywood though that won't hurt. It will add a little more weight, but I would cut them out following the pattern. You could even use it for the bow/stern plates, but some scraps of 1/2 or 3/8 would work better.

Cutting the plywood sheet in half for transport would be better, lay out some photocopies on the wood before you cut it to make sure you have enough, both Yost's I've constructed have been cut out of scraps. The largest form is only 24" or less across at its widest point.

Epoxy it all if you want. Oil is quick easy and relatively cheap. 2 coats of boiled linseed oil, and go. The 5 year old oiled frame is as good as new.

Hatches are cool, but in a SOF you can put stuff in from the cockpit area. You MUST, MUST build and install some float bags.

Search the forum for advice on scarfing stringers. Lots of info here. 2 scarfs per stringer work, try to stagger them if you can. You can use any softwood, pine, spruce, WRC, NWC, basswood...... Pine works well, again with a little weight gain. If you find rough wood that works for you, use it and just smooth it up with your sander.

A SOF is very forgiving. Use a guide on the jigsaw or circular saw to assist your longitudinal cuts and don't sweat it. If they are a little wavy between the uprights, put the wave towards the center of the boat. The Eskimos built these with round unfinished tree limbs!

You want the grain to run down the length of the boat. Put you board (12') up on a support about a foot high on each end and then stand in the middle of it. No breaks, good to go. The cut stringers will bend much more easily.

Hopefully some else will get to you with skin ideas, Bill has posted about a fiberglass skin method that sounds very robust.

To peak some ideas,

https://plus.google.com/photos/117559716817437712203/albums/5160343645377685937

https://plus.google.com/photos/117559716817437712203/albums/5160343645377685937

If they can do it.... you can to