Breeding red shrimp

Actually what I've done in the past is to use water from another tank that's already got fish in it. Is that a good idea or not really?

Not really, the bacteria you want don't live in the water, they attach to surfaces. So they're living in the filter media, on the tank glass, the substrate, the decor, plants etc. So water doesn't help, but transferring some filter media or even some substrate can help speed up the cycling process, since you're placing some of the bacteria you need right in there, and then it's a case of growing the BB colonies to the right size for your new tank and bioload.

Transferring some filter media/substrate is called doing a seeded cycle. You still cycle as described in the fishless cycle thread, but it's usually a faster process if you've seeded the cycle.

Have a look at the thread about cycling: https://www.fishforums.net/threads/cycling-your-new-fresh-water-tank-read-this-first.421488/

Ok. Thanks
I will continue the way I'm doing it then.

You have plants in the tank and shrimps don't have a heavy bioload. I would wait until the plants are actively growing so that they are able to use all the ammonia made by the shrimps.

When I had shrimps in a tank with fish I did not use a specific shrimp food; they lived on fish food, algae, biofilm etc. Now that they are in a tank on their own, I do use Hikari shrimp food, though no nearly as much as they suggest.
My shrimps are now in their own tank. This used to be a betta tank, but after the last one died I decided to move the shrimps over from my main tank. The filter and substrate are the same as when the betta was in there, but I threw away the decor and moved some wood and moss over from the main tank, and got a couple of new plants as well - including frogbit which now just about covers the tank.

I've added a couple of pieces of wood as well.
Thanks for the advice by the way!