does gambling good items depend on char level?
does it matter what act / difficulty i'm in ?
any tips would be appreciated

higher level = better
care which act or another ding..

does # of people in game effect anything ?or difficulty?

Only Char level !

character level is what is important. of course depending on what item you want high level doesnt mean better because there are more mods available to spawn at higher levels.

Get the highest level character you've got, preferably Level 86+, and gamble in Hell at Gheed or Jamella.

Character level is the only thing Gambling gives you an item -5 to +4 your character's level. An amulet needs to be ilvl 90 to be able to spawn +2 skills. Being 86 will give you a 1/10 chance at the possibility of spawning a +2 skills amulet while level 95 will guarantee you having the chances of spawning a +2 amulet.

Only other thing that indirectly affects gambling is difficulty, only because you can vendor back for max gold.

I like how everyone instantly recommends getting to level 95 and gambling +2 amulets.
Gambling doesn't end at +2 amulets, its just the 1 thing most people can manage to remember about gambling.
There are a variety of other interesting things you can gamble, I'll enlighten you below:

No matter your level, you will have a 10% chance of getting a rare.
The level listed is when you start having a 100% chance to unlock those modifiers.

The cost to gamble depends on your character level, here are some average prices for belts/boots. My recommended in italics.
Level 25: 4k
Level 35 : 7k
Level 45: 10k
Level 55: 18k
Level 65: 28k

Belts

You wont be able to gamble for a belt with 16 slots, but you can go for a 12 slot Belt or Heavy Belt.

Level 23: 30% tri-res | 24% fhr | 20 life | 5 Strength
Level 35: 30% tri-res | 24% fhr | 60 life | 9 Strength
Level 47: 30% tri-res | 24% fhr | 60 life | 15 Strength
Level 63: 30% tri-res | 24% fhr | 60 life | 20 Strength

Boots

You want to gamble for Boots or Heavy Boots

Level 23: 30% tri-res | 10% fhr | 10% r/w | 3 Dexterity
Level 30: 40% tri-res | 10% fhr | 20% r/w | 3 Dexterity
Level 39: 40% tri-res | 10% fhr | 30% r/w | 5 Dexterity
Level 51: 40% tri-res | 10% fhr | 30% r/w | 9 Dexterity

Level 42: 40% dua-res | 20 mana | 10% fhr | 30% r/w | 5 Dexterity
Level 57: 40% dua-res | 40 mana | 10% fhr | 30% r/w | 9 Dexterity

Rings 50k each

Level 61: 30% tri-res | FCR | 30 life | 60 mana | 15 Strength | 15 Dex | 6 LL | 3 ML
Level 63: 30% tri-res | FCR | 30 life | 60 mana | 15 Strength | 15 Dex | 6 LL | 5 ML
Level 73: 30% tri-res | FCR | 40 life | 60 mana | 15 Strength | 15 Dex | 6 LL | 5 ML

Amulets

You can decide when you want to start gambling for +2 amulets based on the cost.

This is how much gold each rare +2 possible amulet will cost you to gamble on average ( not guaranteed to have +2, but guaranteed to have a chance at it )

86 = 6,300,000
87 = 3,150,000
88 = 2,079,000
89 = 1,575,000
90 = 1,260,000
91 = 1,045,800
92 = 899,640
93 = 787,500
94 = 699,999
95 = 630,000


I have characters dedicated to gambling for boots/belts. There might be other interesting gambling hotspots but these are my favorites.

very helpful! thanks!

Change anything if you gamble from gheed instead from jamella ?>