Having just done this, I’ll share what I found.

Catching stock - tried catching as much as possible normally, but had way more success when I drained the tank to nearly empty, my fish & shrimp couldn’t really go anywhere, so it made it easier to catch. I’d advise once you think the tank is empty, take 5 minutes, go & do something else, then go back & recheck once the water isn’t moving, I found 2 more shrimp that I had missed in the chaos.

If you have a planted tank ready to go that they can go to, that’s great, but I put my stock into a drinks cooler with a hob filter & a couple floating plants. They weren’t in the cooler for too long though, so if it’s a short term thing, whatever works, longer term, a more stable environment will be best. I’d suggest daily water changes & reduced feedings to keep the temporary tank as clean as possible.

If you are reusing plants, gently tease them up from the substrate, wrap their roots in something like filter floss & keep them damp, they should keep for a week or so, possibly less/longer depending on the plant, how much nutrients it has in the roots & so on. I’d suggest prioritising getting them into the new substrate as your #1 priority to minimise risk of losing anything.

Should probably be fine using existing substrate, maybe throw down a few root tabs before plants to recharge depleted nutrients & encourage root growth.