Battery building best practices? 18650 packs

I've seen several articles and videos on batteries for ebikes and power walls.

The techniques are similar but some of the details vary.

Spot welding battery terminals to nickel strips seems to be the best way to connect to the cells without damaging them with soldering iron heat. On the other hand, I'm not sure how much I like that nickel strip as a conductor.

BMS sounds like a good idea but it also seems like some BMS may cause more problems than they solve.

Who here has worked out the trade-offs in battery construction and figured out the best construction methods for a DIY pack?

Lastly, I'm getting a case of new old stock batteries. What is the best method for testing and balancing them before I assemble them in to a pack? I don't want to spend a fortune on a charger/tester but I also don't want to spend a month testing batteries.

Theres' lots of threads about 18650 pack building, if you read around. Many of the threads with 18650 in the title are relevant, so that's one way to find them; the titles generally let you tell which are the ones you're after.
https://endless-sphere.com/forums/search.php?keywords=18650&terms=all&author=&sc=1&sf=titleonly&sr=topics&sk=t&sd=d&st=0&ch=300&t=0&submit=Search

The same thing applies to charging, balancing, and BMS use (or not).

There are some links in the battery tech sticky index thread that may help, too.

Everyone has different opinions, so you should look at the various stuff that's actually been done, and how it worked out for them, to figure out which will work best for you.

Just go for it and learn as you go, get some dead cells from some where (old laptops or power tools) and practice on them, my two cents is this get a really hot soldering iron 300w one from eBay or aliexpress and use that don’t spotweld unless you have a really good one, spotwelding is a good idea but the spot welders suck, plus the soldered battery contacts have a greater surface area and are more machinically stronger then spot welded tabs, also get some .2 - .5 mm copper sheets and cut them out with scissors or a paper glaten then drill or punch a m3 hole at the place you want to solder that way the solder goes through the hole making a really strong connection