No matter how much power i give to turrets they never work 

I just tested with the following, and the turret was powered as soon as it was deployed.

"autoturret_deployed": {
  "RequirePermission": false,
  "PowerAmount": 10
},

Perhaps you have another plugin which is conflicting?

how do i add the gun and ammo to the turret if the turret turns on automatically before i can add them >>

You can use the plugin Always Lootable Turrets. Note that it has a side effect of removing the red/green laser, and making turrets quieter, because it makes clients think the turret is off.

You could try Turret Loadouts, but it allows free items so not ideal for all servers. You can configure the free items to be locked away, though, to reduce economy disruption.

Players can also just temporarily plug something in that has no power, such as a branch, to configure the turret. I know this isn't ideal, but this plugin just isn't designed for this specific use case.