Mike,

I paddle a 19' stitch and glue Baidarka designed by Eric Schade of Shearwater Boats, at 21" wide it is narrower than many boats. Prior to and during the building process I was unsure as to the suitability of the kayak for fishing due to it's narrow beam. I needn't have worried. I've spent many hours fishing in the kayak, and have caught lots of fish from it, nothing really huge yet an 8 or 9 pound northern pike would be the largest so far. I don't have a rudder on my boat and have not felt I needed one, steering in 'most' single kayaks in 'most' conditions can be done easily with paddle strokes. But whether or not to install a rudder is a personal decision. If yo decide to install a rudder there are a few modifications that will have to be done during the building process keep that in mind as you build. If you want to go with a trolling motor as you mentioned the same applies, see the photo below. If you are thinking of a bolt on trolling motor like you have in a fishing boat that would be a little different, although not impossible with an outrigger or something. If you decide to go tht route it would be a new twist but I'm sure you will get lots of great suggestions from PGJ, Mick, and other kayak brainiacs on this board.

I keep my GPS in my vest pocket or under the front bungees(with a tether just in case), I have my eye on a portable fish/depth finder but it's a little pricey and I haven't saved enough Canadian Tire money up yet to pay for it.

My fishing set up is a rod holder that the base fits under my front bungees that holds my rod nearly horizontal, on a slight angle running nearly parallel to the keel of the boat. My line enters the water along the shear near the front of the boat and stays right beside the kayak when trolled so as not to interfere with paddle strokes. With the rod right out in front of me I can easily see when a fish hits or when I catch bottom or weeds.
A vest with lots of pockets is an essential piece of gear to keep pliers and other gear close at hand. A net can be stored under the back bungees.

You'll come up with your own system, one that works for you, after a few outings. Building the boat and rigging it for fishing is as much fun as the fishing.

Enjoy, and keep us posted on your progress.

Ken