Batteries are designed and sized first on the type of discharge, for example short duration high current such as engine starting batteries or for power distribution longer duration low current such as you might use in a solar application. When purchasing batteries you determine you load (or expected load) and duration of support time you require. You need not concern yourself with. The manufactured data is based upon your expected shut down voltage, the lower the voltage you discharge a battery to the more capacity but this shortens life. For long duration discharges the typical shut off voltage of the system is 1.75 Volts per cell.
If you are serious about this get the PRPOER BATTERY for the application, the plates in a battery are designed for the particular application.
As for sealed versus flooded, the industry is moving away from flooded cells in smaller applications as there is less maintenance and handling of the open jars and off gassing is not as big an issue.