Pyramid plunder to 90, then do dwarf traders to 99. That's my advice. Dwarf traders gives slower than monkey knife fighters per hour but it's less tedious. All you have to do is click on the same spot over and over again.
Heist:
You need 2 accounts, your main account joins the robber team, your other account joins the guard team. You need a friend with two accounts as well.
Game starts once there are 2 players on each team.
Pickpocket a random NPC in order to get his/her disguise. Find the building with the chests in it. The building with chests is nearby the guard spawn so its clever to take a quick look at your other accounts minimap in order to get an idea of where the chests are.
You dont have to do anything with your other account, its only used to start the game, make sure it does not time out though (more than 5 min afk).
So ye, pickpocket a random NPC to get a disguise, find a chest and loot it, bring the loot back to the ship where you started at the beginning at the round and deliver it by talking with the npc on the ships deck.
Go back and loot another chest, bring it back to the ship but do not deliver it till the timer is at 15 min. Once the timer hits 15 min both you and your friend should deliver your 2nd loots, once its delivered you win the game.
Repeat.