Is it realistic to think that the freelance path can be used in a way that I could work for a limited amount of hours while still having a decent amount of income to sustain myself ?
Of course. Many people do it successfully and happily. Given your financial background and needs that looks entirely viable.
If so, how much time would it roughly take to get to the point where I could decide when to work when I need to (if that's even a possibility)?
You need to figure this out yourself: Create a business plan and a budget. First, understand the cost of being self employed in your local legislation. You are not getting benefits, so you need to cover health insurance, self employment taxes, retirement savings, etc all out of your own pocket. Then figure out how much net income you want to make and how much percent of your time you want to work. From that you can calculate your target hourly and check if that's reasonable. In the US a "ballpark" number for this sort of thing is 2-3 times your employed hourly rate, but it highly depends on your locale.
Then start trying to line up business. This may take a while, so you ideally you want to get started while you still have a steady pay check. This will give you a sense on how easy/hard this will be. A good network REALLY helps with that. Once you feel you have "critical" mass, you can take the plunge.
Then track to your target work load. If you are working less than planned, ramp up the sales/marketing activities. If you are working more than planned, you can spent all your extra time on non-work activities.
Over time your network will grow and things will become more steady. If you are in the lucky position that you get more business than you want, you can hike up your rate and work even less.
And if it doesn't work out, you can always go back to being employed. A stint as a freelancer looks fine on the resume.