There is a huge selection of great kayaks out there now, many designed specifically for fishing. My advice for a fishing platform is to go with a sit-on-top design and then dress according to the water temperature.
All of the major manufacturers have a range of sizes from compact 12 footers (which are very nice and very functional) up to 16ft. The longer boats are faster and give you a drier ride - bear in mind that 'dry ride' is a relative term. As new models come onto the market, a lot of folks upgrade and sell off their existing boat - often at a very good price.
When sight fishing, look over your shoulder from time to time, you never know who's behind you