When crafting, your level and the item level get halved (both results are rounded down) and the sum is the new item level which sets up which affixes are possible. There also is a crafting penalty regarding the level req. I'm not a crafting expert, so perhaps somebody else can tell you more.
It doesn't matter in which difficulty level you gamble. Only your class level is important. MF is not a factor, but a Gheed's charm reduces gambling prices.
I'll assume you're aiming for amulets with +2 skills. As noted, an amulet must be ilvl 90 to have a chance at +2 skills. Gambling amulets with a lvl 95+ character guarentees they wil have ilvl 90+. For the crafting part, if you gamble with a lvl93 character and then craft the amulet with the same character, you're guarenteed of crafting an amulet with ilvl 90+ (and a chance at +2 skills).