Studs / headless bolts are the "best" as there is no twisting force when you tightening the nut.
For loctite, there is special that is conductive, according to their site.
I have no knowledge of numbers of threads being standard, most nuts are 4mm for M6 thread.
The 6mm in the terminal should normally be sufficient, and using studs the 8Nm torque (see manual)
should not damage the aluminium thread.
The cells should be compressed together with 200kgf on the flat sides, this to prevent delaminating.
My 280Ah look like they are vacuum, dented slightly inward.
My 152Ah never looked like this, and are slightly bloating / delaminating as I did not compress them together...
Lesson learned..
Not to make that mistake again
I read that professional installers (for UPS in telecom houses etc) use silver conductive paste.
I found on Amazon, but too expensive to get to Thailand.
I now use silver paint, the kind you use to repair PCB lines.
It fill all the tiny gaps in the terminal and bus-bars, and acts as some protection against galvanic corrosion.
Be sure to clean the aluminium terminals and bus-bars till they are as free of corrosion as you can get them.
Aluminium oxide fast, you have enough time after cleaning to mount.
Just don't clean 32 cells and start installing afterwards..
Better small portion of 4, install, next set.