Early rehousing plan

I am thinking about what i could use as enclosures for my three B. Albopilosum slings after they grow
out of there small deli cups in the coming weeks, so would those plastic containers that salads come in
work as an upgrade or should i find something bigger?

It would help to specify the size of the slings in question. The word "spiderling" is used to describe a very wide swath of young tarantulas and could mean anything from 1/4" to 2" and obviously that is going to affect a recommendation.

I use condiment cups for very small slings of 1/2" or smaller, moving them to 16 oz. cups until about 2" and then they're moved onto the regular sized shoe boxes.

These are my containers of choice between the condiment cup and permanent home. Got mine at a container store but have seen them at Joanne's, too. I cut out the top of the screw-on lid and hot glue a shower drain cover on top. Since they stack, you could probably add more vent holes on the sides instead of the top and stack them. (Wish I had done that - I could use the space!)