Best practices in voltage before stringing cells

so I have finally ordered my 18650 cells and BMS. Are there any best practices for cell voltage before I start stringing them together? should then be at a specific voltage range? I assume that voltages should all be pretty close since I ordered reputable cells from a reputable vendor. I am of course going to double check them first. I have read a couple of suggestions that the voltage difference is important before putting them in their groups. Is that the case and if so, what charge/charge difference should I ensure that they have?

You want them all to be the same. It shouldn't matter what voltage they're at, as long as they're all the same, or very close (within like .02V max).

When you connect cells in parallel, a lower charged cell will draw power from a higher charged cell, until they are equal.

There's nothing regulating how fast this energy transfer happens, aside from whatever resistance from the connections between them. It's therefore possible to greatly exceed the charge rate capacity of the lower cell, causing permanent damage to the cell and possibly causing it to overheat and catch fire.

Awesome, thanks. This is exactly what I was looking for. I'll test them all. If they are off, then I'll get them in range before linking them.

If you've ordered new cells from a vendor, they should all be at the same (+/- 0.01V) shipping voltage - usually sub-3.7V. I normally see around 3.60-3.64V on the stuff I order, depending on the particular variety of cells.

If they're all over the place, they're probably not new, OEM cells, so complain.

In general, you want to be sub-50% SoC when building packs, and lower is better. Shipping charge is fine (3.6V or so on a 3.7V nominal chemistry). Screwing up at 3.6V is exciting, probably will destroy the pack (depending on how you screw up), but probably won't catch fire. Screw up at 4.2V, and, well, you're building the pack outside in a non-combustible area, right?