Starting Battery size

[photon_trap]

Hey all -Planning my starter battery side of my battery charger (Kubota EB300 and 555 Alt./Balmar MC-614 Reg.) and was wondering what size battery to use.
I suppose I don't need a group 24 for this (?) but I am unfamiliar with smaller group sizes and since I plan to incorporate a battery holder into
my frame I want to size it correctly for a common group size of more than sufficient capacity. BTW I live in So Cal so extreme cold weather is not an issue.

Also, while I plan to use this as a DC battery charger, I may someday want portable AC power. Is it feasible to use an inverter attached
to another onboard battery or is there a better approach?

Thanks
Jeff A