2. If I recall correctly, 12v batteries with high CCA have worse DoD longevity (and vice versa.)
Starting batteries with a high CCA rating have thinner plates with a larger total surface area, to support as large a number of chemical reactions as possible to produce those amps. Deep cycle batteries have thicker, more robust plates for longevity.
The battery goes under the hood, so I don't think there's any concern/need for vent tubes.
Right. Vent tubes are for batteries that are located in places where any vented electrolyte would cause serious damage, or in remote locations that don't get washed or cleaned. Priuses use them because of the location of the accessory battery in the rear cargo area..