A great way to earn more coins quickly is to go to the shopkeeper and use the liquidate option. This will automatically figure out if you have more than five of an item, and then will sell all but five of each item (one for each party member). Go there and sell anything that you don’t need anymore (even if there is five or less of it) to make extra money, as well.
You need a specific reputation for each unlockable character, not just a specific type of soda. You need both. Sodas will boost your reputation, but you’ll have to spend money to boost it in other ways. The fastest way is to buy the Decor upgrade for your tavern, as that will add 50 to your reputation. Most other upgrades (tables, stools etc) will add to that.
If you have the coins available to get from watching an ad, but you are not connected to the internet for some reason (I.E. you are on a plane) tap anyways. The screen will go dark and the game will say “Ad loading…” for about ten seconds. Then the notification will disappear and you will get all of your 750 coins even without watching the ad
Buy the bed and you can reload the characters that appear in the tavern. A good trick to do is to hire all of the good characters that you want, then reload with the bed so that the good characters come back. Then buy the good characters, fill up your party, and go questing.
Once you unlock the healers, be sure to add at least two of them to your party, and make sure they get the strongest equipment. When you have them, they will typically only heal if you have a character with less than 1/3 of their maximum HP, so it tends to be best to sometimes knock the game out of auto battle mode, use healing moves, then go back into auto mode.
After you beat level 50 of the dungeon, you will unlock VIP mode. This mode has some extremely expensive items that the tavern owner will not sell to you, so go here if you want to unlock the most expensive and most powerful heroes far later on in the game. You can also unlock the ability to warp past level 100 in the dungeons immediately after going through the portal, without having to fight through all of them again.