Hi and welcome to my Bankplank guide.
I will go over runes skill sequence and builds.
Enjoy :)

Flash is necessary for 95% of all champs in league Bankplank is no exception.
I usually go for tp however u can still go ignite or even heal if you really want to.
Tp is great for getting around the map and helping teammates. Even with the nerfs I think that Tp is sill great for patch 4.12.

Farming as Bankplank is pretty easy once you get som cdr and some points in your q. You will generally want to use your q to farm which can give you a gold advantage, over the enemy laner.
However try to only aa in the early game as it does take up some mana which you dont have a lot of.

With masteries i tend to stay away from the defensive mastery treebecause your goal is just to get that gold regen from the utility tree as well as getting ad and CDR on the offensive tree. You already have decent poke against melee champshowever if you dont feel like going so many points in the offensive you can put some points in the deffensive.

Your runes are really up to you, i like to go with gold over per say health or armor as dat money is what were going for with bankplank. For marks i even sometimes go with armor since you dont really have a lot of armor or health you would have as if you went with health or armor seals.
With quints there is really no choice as they give you the gold regen you need to get those items.

Pros
You arrrrre a pirate!
Decent laning phase
Gain tons of gold quickly
Global ultimate
Funniest champ in the game
Can remove cc with W
Movespeed-buff to your allies (E)


Cons
Is arguably the worst champion in the game
Bad teamfighter without ult
Bad late game
Ultimate is random, can lead to losing kills
Struggles against gap closers

Even though gangplank will never be in the meta with his current kit i still play him as i think he is extremly fun to play, however he doesnt have a lot of payoff. Overall his kit has more weakness than strenghts, as a gangplank s1 main it hurts to say but its the truth.