Hi lockhart52. Congrats on your decision to get a boat. I think you'll find that a 12' boat gets pretty small pretty quick, but a 14' is a nice medium size and you should be able to carry 2-3 adults and gear comfortably. As for hull design, that mostly depends on the conditions you primarily boat in. Semi-V and/or V-hull vessels have better handling in chopper, or rough water, but usually require slightly deeper water to operate in effectively, whereas flat bottom hulls are very stable in calm water, but tend to slap up and down on the surface while underway. I have a semi-v hull that is a nice compromise between the two. It is angled at the bow to help cut through chop, but eventually flattens out towards the stern. I think you'll find a width of about 5' is what you'd like to have to. Jon boats are very often listed using a series of 4 numbers which indicate its length and width. For example, a 1452 jon boat is 14 feet long and 52 inches wide and a 1336 would be 13 feet by 36 inches.
Once you've picked a hull, the rest is only limited by your imagination and budget. There are only a few rules when it comes to these old tinnys. 1) NEVER use PRESSURE TREATED lumber as it can cause electrolytic pitting. Instead use jigh quality, exterior grade plywood from Lowes/HD. Auraco brand is good and readily available. Once you have the wood you'll need to seal it. You can either use wax-free polyester resin and fiberglass mat, or 2-part epoxy. Most folks tend to got the epoxy route, but it is a bit more expensive. If you can't/don't want to use either of these methods you can use Spar urethane and/or Porch Paint. These won't waterproof the wood, but should give you several years of good use. 2) Use aluminum replacement rivets and/or stainless steel hardware throughout. That's really about it. The rest is up to you. Keep us posted. We love pics. Good luck. Happy hunting.
btw.....Ilike the first 2 choices. The first one looks like a complete package, but the second one is a blank slate that you can make your own. I'd probably go with the empty hull and make it my own, but I like to tinker and fiddle with these old boats.