1-If in my first roll i got 1 gatling dice and i kept aside, then in my second roll the result has 2 gatling dice , does gatling attack triggers automaticly since there are 1 gatling dice kept aside and 2 in the pool or do i need to keep the 2 gatling dice in my first reroll beside the 1 gatling in my original roll to trigger the gatling attack and resolve it at the end of the turn?
2- does gatling attack when activated will end my turn or i do resume my turn after the gatling attack?
Besides the Arrow (which you take immediately) and having 3 Dynamite (which ends you turn), you do not do any of the other actions until you declare you are down rolling (or have rolled 3 times).
So having 3 Gatling guns does nothing unless that is your final result. You could still re-roll, having not activated them (if you had leftover rolls).
Once you have your final roll, then you have to resolve them in the order listed in the rules. There is a hierarchy to them.