I would want a schedule and restrictions (you said supervised visits) in writing from the start.  It is a lot easier to make some verbal adjustments later when some of the dust has settled.  As far as a 'as wanted' schedule, that would wreak havoc on any planning or scheduling.  When the kids were younger, I knew which weekends I could take them to a barrel race, horseshow, or rodeo without having to jump through hoops and getting the X's 'permission'.  I knew when I could sign them up for dance lessons, softball, etc.  As they got older, they started telling him when they were going.  Even after 17 years (we separated when I was preg) I got reamed for a youth rodeo finals that was 'on his time' that he didn't know anything about.  He had the year-long schedule pinned to his kitchen wall!

If you are concerned at all about his ability to 'parent', I would want the strictest custodial agreement you can hammer out right now.  You can always be more generous if you want but should you not trust the situation, you have legal support.

This is my plan, very strict arrangement at first.