Lead batteries are a lot heavier than the modern LiPo batteries.

24V motors, you can do that with 2 cheap 3S , or 1 less cheap 6S LiPo pack from any cheap supplier, like this one

No, you don't need a battleswitch.
According the FRA rules, you need a removable link. A piece of wire/connectors that can be removed without the use of tools.

Peak power, it's the max electric power a part can deliver or withstand for a very short time.