I've built similar 18650 power packs. My estimations are rather conservative because you need to take into consideration of not just whether the metal strip can handle the current but also the temperature rise of the metal. I try to keep things to around a 10 degree rise or lower over ambient of 25 degrees. This insures that the strips won't melt the surrounding plastic. Specifically the battery covering.
You can use a PCB trace calculator to give a ball park estimate of how the metal strip will react to different currents.These of course are for copper traces, but if you stay on the conservative side it will work as an estimate for nickel.
https://www.advancedpcb.com/en-us/tools/trace-width-calculator/ Type in the current requirements and thickness of the strip. For the length I put in 18mm because that's the approximate length of strip between each 18650 cell of the 7 parallel cells. I try to keep around 10 degrees over ambient. Which would be 35 degrees total temperature of the metal. That keeps the surrounding plastic safe from melting.
Use the Results for External Layers in Air for the width of strip.
Just make sure you set the measurements to what you prefer. millimetres, inches, Celsius, Fahrenheit
My calculation came out to 7.64mm width, so 8mm strip of .15mm nickel should be OK for 30Amps
You can play around with the calculator to give an Idea of what to expect with different thicknesses and currents.