I loved it but the leveling up and such were basically non existent, the methods provided were one time use and it took forever to save enough coin to do anything. 

The worrier offered at the start of the game was the only one with stats able to handle a simple slime, out of 30 others that came in none of them could stand up against a simple. 

Spending money on hiring new guys felt wasted. None of them after the start up player could beat a single slime because the levels were so low on them.  You never make the money spent on them back.

I loved the whole concept, but after a while of playing, it became a little repetitive as you couldn't really use the other features or when used they didn't work out well.

The potions should not be a one time use, perhaps have a time limit to them, worth the material and coin spent to make them. You only get a couple coins per battle (Nothing near the cost you pay to craft the potions)  and the potions wear off as soon as the battles over, never to be used again.

Hiring, the levels of each character should be staggered that come into the guild, they  should not all have the same level as those I came across did (which was Attack level 3), or they all should at least be strong enough to fight off a simple slime , to at least over time, make up the money you spent on them.