As Zerienga already kindly replied farming production runes especially blends is a good income.
What else i can think of is daily items for low level chars, also to sell honorpoints (you can get this from guildcastles minigames) if you have time maybe pick up crafting (recipes like heropots/stimulant).
And yes if the level of mob is too low compared to yours it means less loot.
Hopefully we will see more costumes in the IS in the future
Offtopic, but... :claps: for new GM's first post.
On topic: Crafting and Pet Crafting would probably be a smart idea, especially if you take up alchemy. The biggest selling potions are Hero Potions (a rare recipe drop, especially since Goblin Mines doesn't give loot off of mobs), Touch of the Unicorn (a manageable to find recipe drop), and Strong Stimulant. Currently, by farming your own Blend Runes, if you have the appropriate level of pet crafting, you spend about 600k gold to make 4.5 stacks of Unicorn Potions which can sell easily for twice their cost up to 3 times their cost. (Don't know about how many stacks you can get of Strong Stimulants or Hero Potions with this method, but cost to make would remain the same.) I usually set up 2 other accounts with completely empty bags and fill my bag with the pet crafting tools needed, then turn on the addon Pet Auto Craft at the mat's needed production equipment and set my stuff to refine in the (forgetting it's name atm) as a list. After about 17 hours (estimating here based off of memory), I have enough mats to make 4.5 stacks.