Yup, it sounds like from what you said that altitude would be at your discretion. If you were cleared for the Arrival into the airport you could follow the flight path for the arrival but you can't descend to the chart altitudes until ATC either clears you down to them or clears you for the Approach. So if you were on an Arrival and then got cleared for the Approach, you could descend down to the minimum altitudes on the Arrival chart, as well as the other minimums you mentioned such as MSA as you come to them.