I agree with Severne, probably 2.5 quarts. You might think about buying a gallon, it`s cheaper that way if you have a use for it. I think S3 recomends 3 coats. I got my best results with a badger hair brush. They aren`t that expensive, and of course this stuff is water based so clean up is a breeze. Joe Greenley recomended the badger brush and for me it made a real difference. Wiping worked also, but you`ve got to thin it a lot more than S3 recomends, so it will probably take much longer to build up a finish.

Having said all that let me add this caveat. The primary attributes of this stuff (IMHO) are it`s rock hard finish, fast dry time, (You can do your whole boat in one day easy), no sanding, and water based. It doesn`t look quite as nice as a really good varnish job, but I think it`s the perfect thing for a "working" boat, that is, one that will see a lot of use.
If however the finish of your labor of love is really important to you, if you built a trophy, a piece of fine furniture, you should probably go with varnish. Have a pro spray it on for best results.