You said a lot. And I agree with everything. The only problem is that no matter how much we try to curb our excessive spending habits, there will always be a solid excuse for us to go back to them. It's like a spirit. Money must be spent.
One mistake people mostly make is going into the wrong relationships. Your partner should be able to help instill discipline in terms of unnecessary spending. Unfortunately, a lot of partners would even encourage you to spend even more than you normally would have. And you'd have no choice, all in a bid to please and not to offend them.
RE: Financial mistakes to avoid in your 20s.