I'll refer you to other readers on the warranty question. You could always call Bennington Customer Service in Indiana.
As far as batteries, you're likely to get a number of answers. The first question is whether you have trolling motors or large audio power boosters to power? If you have neither, I would just use an automobile style "starter" battery from one Autozone/Advance/O'Reilly's--as a cost savings. I've had'em last 10 years, and I've had them easily start a boat that hadn't been running in 2 years. 650 amp hrs. would be a minimum size.
Deep cycle batteries used by trolling motors don't seem to have the lifespan of a "starter" battery, and they're generally expensive. But they are required in recreational vehicles, however, hooked to a converter to run 12 volt lighting and a water pump(when 110 volts is unavailable.)
I'm sure the Optima blue top deep cycle battery is a fine battery, but it cost twice what you could purchase a regular battery for. Optimas have their place--when a battery's going to be forced to undergo a few g's (offroad racing) or if they need to be installed in a tight place or funny position--like on their side.
Good luck!