Probably start with paper prototyping. Throw away your computer, we're doing this old school! If the main game action you're doing to track finances, assign tasks, and watch stats increase, then try to play your game like a pencil-and-paper game.

Write up a notecard with each of your characters and then just "play" the game. Ask yourself "ok, the game gives me this problem, what do I do?" Assign tasks. Update notecards with stat increases. Simulate any randomness you need with a dice. Skip the turn-based combat for now, and figure out some other way to resolve that conflict.

When you feel it's getting somewhere interesting, grab a friend, sit them down and say "ok, you're playing my game. Here are your people. Here is the problem. Here are the rules. What do you do?" and have them play your game. (While you just sit there and answer questions, and tell them how the game responds to whatever they do.)

This is how you fail fast - you do the bare minimum needed to test out the core of your rules, and do that. And then you just start trying it.

Best of luck!