I'm looking to gamble +2 circlets/tiaras/diadems/cornents. Which level should I be to maximize my possibilty of htis?

higher the better but anything 80+ is fine

Circlets : level 92 exactly
Coronets : level 87 exactly, unless you want to gamble diadems via coronets (and then : level 99).

For gambling circlets....
You need to be level 95+ to maximize your chance, and a minimum of level 86 to even have a chance to gamble a gg circlet.
+2 class skill on a circlet requires an item lvl of 90.
The item lvl of a gambled item ranges from -5 to +4 to your character level.
95 - 5 to 95 + 4 = 90 to 99 on a gambled circlet from a level 95 character.
86 - 5 to 86 + 4 = 81 to 90 on a gamble circlet from a level 86 character.

No.
87 for circlets, 82 for coronets, 77 for tiaras and 1 for diadems (due to magic levels and quality levels).