You must upgrade the personal "free case" level by making deposits on a regular basis.
To get Level 1 (and be allowed to open free case), you must deposit at least $3. To move to:
to Level 2 you need to deposit extra $25
to level Level 3 - extra $50
to Level 4 - extra $75
to Level 5 - extra $100
For example, to get to Level 5 right away, you must deposit: $3 + $25 + $50 + $75 + $100 = $253
Free case opening doesn't reduce your main $$ balance.
Once a day.
Yes, each day your level will be downgraded by 1 sub-level (each level has 5 sub-levels) unless you deposit daily.