Hi Silas,
My dad got a lot of good tips from Kwin (from eFoil Holland).
Basically, you do solder the tabs together! One side of the aluminum tab is copper-plated. (see picture 1) Use some fine sandpaper to roughen the copper side (picture 2), pre-tin both COPPER sides you are going to solder (picture 3), use some crocodile clips (picture 4) to keep the two tabs (copper side on copper side) nicely together, and use a strong soldering iron (we used a 150-watt one) to heat the tabs until the solder flows nicely together.
We used double-sided tape on the pouch itself to keep (in our case) the stack of 5 pouches nicely in line.
It sounds more complicated than it actually is.
The pack is a 15S1P, and the intention was to use the BMS also for discharging as it was supposed to be able to handle 120 amps.
Unfortunately it cuts out at 70 amps, and so not usable for discharging.
Now we only use it during charging and balancing all the cells.