"When is enough...enough? Will there ever be a point where I'm satisfied with the money I make, or things I own, or things I do? If I decide I'm happy with where I am, does that mean I stop progressing? If I'm never satisfied, I'll probably achieve more, but at what cost?"
Complacent: Showing smug or uncritical satisfaction with oneself or one's achievements.
You absolutely, positively, 100% SHOULD be satisfied with who you are and what you have, but under no circumstances should you ever be COMPLACENT. Being complacent means overlooking serious defects or problems that need correcting. It's a false sense of satisfaction that hinders future progress and growth.
It may feel like these are the only options...
1. Be happy with who you are and never accomplish anything great.
2. Not be happy with who you are and simultaneously increase in achievement and misery.
...but luckily that's not the case!
You can be happy with where you are while looking forward to where you will be. That's the beauty of progress. As long as you're moving in the right direction, you can be satisfied.
So when is enough...enough? When your priorities change. For example, when you have enough money to stop living paycheck to paycheck and decide that spending time with your family is more important than getting a second job, you have enough money.
Be proud of what you've achieved while at the same time looking forward to everything you will achieve. It will probably take a real paradigm shift to begin thinking this way, so give it time. Concentrate on gratitude for what you have while you work towards more.