A few extra pounds load doesn't make a big difference if it's low down. It's your height that is the problem, it raises the center of gravity and reduces stability.

Big guys don't need big boats: extra beam adds stability very rapidly, much more so than length. Length is for speed, if you want it, but you still have to earn it with your paddling, whereas at a relaxed paddling pace a shorter boat can be faster due to its reduced wetted surface. I have a kayak that is faster than my shorter canoe - if I work hard enough - but the canoe is faster for simply cruising.

Additional kayak height isn't that good a thing unless the boat is to be heavily loaded. There is a big difference between a heavy load packed down at the bottom vs a tall, heavy guy who can move around. If the waterline beam is constant (i.e., vertical sides) the metacentric height is actually lowered when the boat is heavily loaded. Don't worry about the big words: just remember that the distance between the metacentric height and the center of gravity is where the stability comes from. If the center of gravity doesn't move down along with the metacentric height as the load increases the boat gets less stable not more. It is not an intuitive thing, but look at the cross-curves published for many commercial designs to see how they are effected by paddler weight. Most recreational kayaks, like racing shells, are sensitive to load.

Stability is nice to have for an activity like fishing. Fishing is a more sedentary activity than paddling so give some thought to comfort. If you need to wriggle around or change seating position to restore feeling to parts you have forgotten for too long, a little extra stability is nice to have. A sitting position that is efficient and comfortable for paddling may not be ideal for fishing. Whatever you decide, try to borrow or rent a similar boat first.

I designed my own canoes because I wanted to learn. I learn best by my mistakes; I don't really want to talk about my early efforts! Boat design is not a trivial thing, so, as a general rule for your first boat do not change any dimensions; it can be dangerous to interfere with the black arts - some of today's designers might have been burned at the stake a couple of hundred years ago . . .

I don't think SOF is the cheapest or lightest method, but it is probably the fastest, and for a multi-chine design, also the easiest. If you use a softer, less stiff wood just increase the cross-section to compensate. Not too much - stiffness varies as the cube of thickness. For wood that is 25% less stiff for example, you would need 10% more thickness - not width. BTW roughcut wood is cheaper and you get the full inch thickness to work with; I don't rely on the accuracy of "finished" lumber if I can avoid it.

A ply boat can be very light (my small canoes come in under 20 lb) but don't use cheap stuff, at least get something that at least claims to be marine grade ply. Like John I don't use epoxy for water-proofing, just 5 coats of latex house paint is fine for a boat like a kayak or canoe that is taken out of the water after each use. However, something better would be indicated for a boat that is going to be loaded with supplies and taken for a long cruise and left in the water after each day's paddle. Speaking of supplies, any canoe will carry far more than a typical kayak.

Strip-building is the most time-consuming of the modern methods, and probably the most expensive if you insist on buying the professionally milled stuff. However, my current build is partially strip-built and on a square foot basis the strip-built portions are probably the cheapest. I used cedar fence planks; I found I could use about 80% of the planks for the boat, with about 20% more lost to knots, way cheaper and more convenient than travelling miles to get "boat quality" wood and the unused planks will get used the next time I fix a fence. There was some extra work for scarf joints because the planks are shorter than the boat but it didn't make a lot of difference to the build time.