I have never finished up a kit boat with just the epoxy they provided in the kit. Of course I tend to patch up other boats, make paddles, and spill a lot. 

There is just enough epoxy for a semi-professional boatbuilder to create a light-weight beauty. There is not enough for someone like me! I think you should buy more epoxy. If you don't need it (and I think you will), it will keep for years and be useful in a wide variety of repairs and projects.

As to varnish, I'm a fervent believer in applying multiple (2 - 3) coats of varnish per day. Don't sand between coats. Just let it get dry to the touch. In two days you can have all of your protective layers of varnish on the boat. Then let it dry for a week or more before giving it a light sanding and a final beauty coat.

That's been my method for my Northeaster Dory and my Shearwater Sport. In both cases the varnish has held up beautifully to subsequent hard use. Here is a link to a bit more discussion of my reasoning.   

My advice on turning the boat would be to get all your "base" layers on the hull first (4 coats, 2 days). Wait a day for it to dry. Then turn the boat over and put all the base layers on your deck. Wait for as long as you can restrain yourself and then put your boat in the water and use it gently. Varnish can take a very long time to dry competely and it is easier to scratch before it is fully dry, so gentle use is important to avoid deep scratches. At the end of the season you can give the boat a full sanding and apply a couple of coats of "beauty" varnish. Let it dry over the winter.   

I agree with the comments above about epoxy.  Better to have too much than to be waiting on a shipment when you want to be building.  I also needed more that was supplied in the kit for my first build.

Regarding varnish, I STRONGLY recommend that you follow the manufacturer's application directions.  Specifically, do not apply wet on wet unless the manufacurer says that you can.  If you have any doubts, call the technical support line and ask.  I did wet on wet on one build and the varnish on that boat ended up very soft and easily scratched.  After calling tech support, I learned that when you apply a fresh coat over a coat that is not fully cured, the new coat prevents the underlying coat from fully drying.  I have used the same varnish (Interlux Schooner) on 5 other boats using the manufacturer's method and they all came out well.

If you use a varnish like Schooner, you can do a coat on half the boat in the morning, allow it to get dru to touch then flip the boat and apply a coat on the other side.  Let it dry overnight, then wet sand the whole boat in the morning before applying the next coat.

Another option is to use a Varnish designed for rapid application.  I have used Epifanes Rapidclear on two kayaks and my GIS.  It is a semi-gloss which can be overcoated after 5 hours without sanding between coats. 

   I never said to apply wet-on-wet. Dry to touch. If you sand between coats you are removing a lot of the varnish you just applied -- though you can minimize that with 400-grit sandpaper. Sanding removes the hard, thin, oxidized coat and exposes "wet" varnish for chemical bonding. The only difference is that you have wasted some of your varnish. 

Mark (and the manufacturers) are right that the varnish will take a long time to reach full hardness (as I stated in my post). But multiple coats of varnish are always going to take a long time to reach full hardness. Sanding between thin coats is a waste of time, energy, and varnish -- in my humble opinion. And the hard finish on my boats is all the proof I need.

Either way you choose to do it, you will end up with a great boat.