: would like to know the pro's and con's about 1/4x3/4, 7/32x5/8,
: 3/16x5/8.

More history than pros and cons. Strip building kayaks evolved from strip building open canoes which used 1/4" thick strips ripped from nominal 1x6 lumber. This lumber is called 4/4 thickness because the roughcut bo3ds *re nominally an in h thick. After shrinking as it dries, and planing it smooth a board actually measures 3/4 inch thick.
Big canoes might use strips which are 5/16 or even 3/8 thick. A 22 foot guide boat that can displace 3000 pounds and carry a moose as well as the guide and the "sport" is not going to be flimsy.

Decked kayaks have structural support from the deck and aren't as wide as canoes. Thinner strips work fine for most designs.

When you cut strips 1/4 inch thick and then decide to run them through a planer to save on some sanding you end up with strips which are thinner. Might be 7/32 or less. Some people plan the design of their forms around thinner strips.
Easiest way to cut weight on a boat is to use thinner strips. The wood parts in a 40 pound boat might be 28 pounds covered with 12 pounds of glass and epoxy. Using wood strips which are 25 percent thinner ( 3/16 rather than 4/16 or 1/4 inch) will cut 7 pounds off of the boat's weight, giving you a 33 pound boat.

Milling a bead on one edge and a matching cove on the other edge may remove a bit more wood and leave you with strips that are actually 5/8 wide, but frequently you'll be quoted the width of the exposed face once you stack a few strips together. The joint eats up 1/8 th inch of wood.

I've used three pieces of 1/4 x 1/4 , ort two pieces of 3/8 x 1/4 to fit in spots where I couldn't twist a 3/4 x 1/4 strip enough to get it to fit. 1/4 inchh wide strips from wood with a strong color contrast make great accents. Looks like inlaid pinstripes.

(2) is 4 oz. glass harder to epoxy than 6oz?

Usually the opposite is true simply because you have 50 percent more material to wet out and a deeper weave to fill on the heavier glass -- but there are some tightly woven fabrics which are harder to wet out. Generally things go better with small batches of warm resin.

(3) what
: is the best method to hold the strips so they are stapleless,

Lots of methods. "Best" for one area might not be good enough for another area. Bungee cords and C clamps can cover a lot of situations. Small scraps of strips nailed or screwed to the frames work cheaply. Stack two scraps so the bottom one pushes the new strip in place and the top scrap overlaps the strip to hold it tight to the frame.

: thanks for helping this 81 year old fool Nick.R.

Too soon old, too late wise. Never too old to learn.
PGJ