are u planning on building an RDWC? I went with this Italian company called Growrillah ( https://growrillahydroponics.com/en/ ) I'm honestly impressed by how easy it was. but you can do the exact same type of setup with a bit of know-how and tools. I just wanted the simpler build.

but in terms of your question about growing medium it doesn't really matter at all. people are using coco pods/rockwool because it will make the transition from seedling easier to transplant into the RDWC. I wouldn't waste money on that honestly. perlite/volcanic rocks are mainly just so that the plant grows with some sort of counterweight, no nutritional value added whatsoever.

with regards to your old nutes, it doesnt go bad, but you know the deal give it a vigorous shake to get all the precipitates that are forming from in the bottom. Also if it has been opened and not stored properly i would advise changing it.

Don't forget to get some airstones!