@zellected well battles for the most part would be based on a few things first of all overall abilities so if someone has an overwhelming advantage 9 out of 10 times they'll win. But for characters made by me I'll be the judge of how fights go so for the most part ill handle it like most Rp's you do your action for the post and I decide how successful it is.
But I do plan on having abit of a stat system though it'd be more of a rating of 1-5 and the stats would be
Endurance: basically health higher it is less likely you will get defeated quickly
Strength: How much damaged your attacks inflict.
Speed: Your characters ability to dodge and land hit's this will affect how likely I let your hit's land so it handles dodging for the most part.
Defense: How much damage you absorb if your defense is higher then your opponents strength chances are they wont do much.
thats roughly how it'd work it's just so I can make decisions on how fights against the current antagonist fought. Also I'll be honest if you ever do player vs player fights I'll actually for the most part leave that upto you just agree on a winner and make it as interesting as you want can be a one punch if you want. Oh also if a pirate your bounty roughly determines your strength so say what your bounty would be even if your a non pirate character so there's a rough estimate.
also for the 4 character types I named a rough starting amount for each would be
Bounty: hunter 14-18 million
Pirate: 13-15 million
marine: 11-13 million
Adventurer: 10 million
Oh also yeah you can use white beards devil fruit wont care but if want his exactly need to wait until his death otherwise just create your own variant with a different name. It isn't too broken just tremors can be handled.