If I may join in...I got into this area in 1996 ; I moved house, moved my orchids - maybe a couple of thousand into my brand new house, and started to watch them die...well, too many of them anyway. So I took a couple of hundred plants and repotted them into 3 or 4 different kinds of compost, one of which was straight Perlite, to see if any one (compost) was better than the other. The problem with Perlite was keeping it wet - at that time I was using it from the sack, without any pre-soak. The plants in that did the worst - over the first weeks, so I tried placing half of them in a tray of water, an inch or less deep ; then I found that if I put a top dressing of ordinary horticultural grit on top, it kept the perlite in place ; within six months I had transferred all of this lot of 50 into this system, and in the next year went on to move another 1000 into it . ( I didn't use it for my Paphs or cymbidiums, or Vandas ( then - but did experiment with these later, when I was getting fantastic results with oncidiums etc ), and I didn't grow many cattleyas at that time. So it was all kinds of oncidiums and other orchids which could be generally classed as South American thin-leaved - Odonts, Oncids, multi-generic hybrids in the Oncid group, Zygos, etc etc.
I did some research on different materials for the compost ; it must be inorganic, so that there is no rot or decay of the compost itself. I made columns, and measured the rate of movement of the water upwardly ( it's capillary attraction of course - so it depends on all kinds of things I can't measure easily - like the electro-chemical series position of the material , grain size,particle shape, (effectively) surface roughness and so on. But I ended up with the recipe: use coarse Perlite ; wash it well to get rid of all dust and fines, pre-soak before use.
Ordinary pots are fine , no extra holes needed - I can see the fun in destroying one Tupperware container, but I wouldn't want to buy pots at that price for a thousand plants !
Best time to put into the system is the same as the best time to pot anything - when new roots are just appearing , that way they will adapt to the different media.Existing roots will rot - at least the end down in the water will, but new roots which grow into the 3ater don't rot. A friend who took samples of my roots said that under a lowish power microscope he could tell which roots had grown in my aquaculture and which had grown in ordinary ( water when the plant is dry) culture - the root structure is different.
I could write a lot more - but about 2003 I wrote ( by request) an article for a French (language) Orchid journal - I have lost the original, but stumbled across a link to an edited version of the English original recently - it contains some decent pictures too - here's the URL - Hydroponics.
By the way I do have a bee in my bonnet about the names used for these kind of cultures . Hydroponics merely means growing without soil . Who does use soil ? a few people growing terrestrials maybe, but not "mainstream" epiphyte growers. And why semi ? Which is why I have at times used the words Hydroculture or Aquaculture ; sorry -I'm a pedant with words ( comes from my working life - now long past, but incurably embedded).