The fuse position will be fine, I think its a good safety feature, provided the nuts are secured tightly. I like to use pico 2A fuses where the balance leads join the nickel strips, in case the balance leads wear through and short each other.
I prefer wider/thicker nickel in the series direction, to reduce wasted power/heat/voltage. I use 30mm x 0.2mm nickel strip laid in the parallel direction, which gives effectively about 21mm width for each cell in series direction. 0.15mm thick x 30mm would be fine, and easier to spot weld if you don’t have a kweld.
Having said that, I just ran some calculations and 8mm pure nickel strips would be fine for most of our efoil purposes, only wasting around 5W as heat if you are pulling 45A cruising current from a 9P pack. Nickel coated carbon steel has double the resistance, and therefore double the power loss as heat, so make sure you have pure nickel. Stainless steel is about 10x the resistance of pure nickel.
Power loss = I ^2 * R
(Voltage doesn’t change loss)
Using test results from here:
Nickel 8mm x 0.15mm strip
With a 350mm length of nickel per series strip of cells (close enough to the length of 13s with 21700)
With 5A per strip - Power loss: 0.60 W Voltage drop: 0,12V Strip resistance: 24 mOhm
Eg 45A with 9p pack, 9 strips gives 5.4w waste heat
With 10A per strip - loss = 2.4w per strip
90A with 9p pack gives a loss of 21.6w waste heat
15A per strip - loss of 5.4w per strip (with 0.36V drop)
135A in a 9p pack produces a loss of 48.6w waste heat