> If the epoxy has cured for more than 72 hours and I wish to apply more, is
> there any surface preperation that will improve the bond?

You need to ensure any blush present is completely removed, that the surface is truly clean, and is roughened for mechanical bond adhesion.

> The boat I am building is the clc chesapeake 17, the instructions tell you to
> apply only one layer of tape on the internal seams.Is this adequate?

Yes imo. Unless you're planning to go white water kayaking with it.

> On the outside of the hull it calls for one layer of glass.is this adequate?

Again yes, for the same reasons above. His designs are deceptively strong. Remember, you're building with arches essentially, and an arch is a very strong shape.

> Should I externally tape the keel line for added durability? If so should I
> tape before glassing the hull or after?

You don't need to do it, but if it makes you feel better, what the heck. Do it after you put the cloth down, to prevent the fun with air bubbles you'd get trying to lay the cloth over the raised edges of the tape.

> Finally can anyone recomend what type of fibreglass I should purchase for
> the hull.

If you've got a place that guarantees lowest prices, like BoatUS, take the CLC price list into them and demand they match it. If they won't, buying from CLC is quite cheap actually, even including shipping costs.