I've been begging for a banking system for years, way back since TS2. So yes, this is a great idea!
What really gets on my nerves is when a family member moves out, they either take everything with them or nothing. If they've worked since they were a teen and created some wealth for themselves, they should at least have a bit of their starter funds. And if their parents can afford, they should be able to gift them some.
But I love all of your ideas. Maybe not necessarily using the credit card, but that's actually not a bad idea. My sims would probably rack up a lot of debt buying things they can't actually afford.
