Naw it’s going in an enclosure…the foam serves to hold the cell holders together and the BMS/charge plug/ switch on the front of the battery.
Had a few other batteries that I had built pop fizzle crack on me and think it in nerved me. I just watched a few videos online of cells going to failure and thought about my small apt and what if scenerios. Just want to make sure all’s good with the battery.
Hmmm…
There’s a lot of scaremongering going around about these batteries, they’re really not as dangerous as people think unless you abuse them 
Some 1mm foam board of you insist on it and just heat shrink will be totally sufficient…
oh yes when it’s wet 
Here’s what I think. You obviously have a spot welder. Why don’t you weld smaller tabs of nickle on for balance leads? Soldering onto the nickle strip over the negative end of the cells is no big deal. They wont short out. But soldering the nickel strip over the positive end of the cells is a bad idea. You could be damaging the casing and asking for a short if/when that pack flexes.
only things i can see here that i might do it to go back with an iron and smooth any solder spikes away. Along edges like that what i’ve started doing is using heavy vinyl tape to separate the balance leads from the nickel all the way down, then i like to bundle the whole edge in a nice 2" strip of black tape before heat shrinking, which allows you to lay the wires out safely away from any potential shorts before they are bound inside the pack.
TL;DR: smooth and rounded solder joints, tape over the nickel before running balance leads down then, tape the balance lead runs before heat shrinking to keep them bundled properly away from any potential shorts.