Totally depends on where you want to fish and what you want to catch. Fresh water, estuaries, offshore, or all of them?
I have a Hobie Revolution 13 and I recommend it highly, although it is nowhere in the price range you mentioned. Instead of paddling you pedal, so your hands are free to fish. I use it offshore extensively.
Wouldn't bother with a motor until you feel confortable with your yak, then decide if you really want or even need it. Get a sounder though, it's a must in my opinion.
Definitely leash everything, period. If you flip over you will lose it otherwise.
Another big thing to consider is how will you transport it? Roof racks, trailer? Salt water is a b****.
Also, sent you a PM with some more info.