Arre you getting a satisfying vape at 70 watts or is it better at 80 watts, why are you changing. Satisfying vape means good flavor, the temperature is neither too hot nor too cold, volume of vapor is good.
I'll start with your second issue, this is call spitback. It's caused by juice on the coil not being completely vaporized. This can occur when you draw to hard and pull excess juice on to the coil, condensation in the chimney, watts too low not vaporizing the juice, juice too thin flooding the coil although you should hear it gurgling if you are flooding it. The difference between 70 and 80 watts may simply be it's happening at 70 but its not hot enough to feel it.
Leaking occurs for several reasons, most of which lead to a loss of vacuum in the tank and results in juice leaking out of the airflow holes.
1) Bad or crimped o'rings
2) Tank not screwed together tight
3) Coil is loose, not screwed in tight
4) Temperature changes causing the liquid to thin out
5) Pressure changes from changes in altitude
6) Not closing air flow when opening the top of the tank to fill it.
7) Letting a tank sit for extended periods of time and the juice saturating the coil and leaking out the air flow holes
8) Cracked glass
9) Drawing too hard and saturating the coil
Tanks require there to be a vacuum inside to keep the juice from leaking, items 1,2,3,6 & 8 break that vacuum.
I have 5 NRG tanks and none of them leak, in fact I encourage anyone that asks for a tank that is leak resistant to purchase the NRG or the Aspire Revvo.
Search the forums and Youtube you will find tons of info on leaking and spitback