space limitations with hydroponics?

This may be considered the most idiotic question ever, but I think it is important and I haven't been able to find a forum that specifically ask what I want to ask so I apologize if it has been asked before. But the question is since the rule of thumb is "at the very least 1 gallon pots for soil grows" what is the very least for hydroponic grows? for example if I am doing a DWC grow with a tote or some other makeshift reservoir that can hold 20 gallons am I limited to 20 plants for that one reservoir or perhaps even more limited than that? I also wanted to ask what is the absolute minimum depth a reservoir can be for a DWC, and is it ok for your medium to touch the water or should it hover over the water. I ask these things simply to understand the requirements for the roots, is full submersion to hard on the roots, or could the roots handle that? BTW if it wasn't painstakingly obvious I am a complete noob who has only ever contemplated growing, I am still in the research phase, I would appreciate any help, Thanks

There's no limit. But once you get so small you get counter productive.
The main point with having a large res in dwc is a buffer as tds and ph will change. Also nutrient solution height will change unless you have an auto top-off.

Some people may refer to this as shallow water culture.

20 plants in 20 gallons, people do this all the time, but they are clone size and later moved.....

ideally the medium should just barely touch the water IMHO

I think you should look into a different hydro route, such as drip or dtw

- Jiji

hmm, interesting. Thank you very much for your opinion and knowledge both are appreciated. Though I was wondering why the ideal is that the roots just barely touch. I think the reason I am asking questions like this is because I have looked into so much about yields that I have in a way become consumed with idea of doing a lot of plants simultaneously in a relatively small environment. Though I should mention for my first grow I plan on doing one big plant and harvesting seeds instead of going through the clone method. I don't just want to suffice in growing, I want to be very knowledgeable about it. I thought about doing deep water culture just because it seemed relatively easy. But, what method would you suggest for growing a lot of plants, my plan was to start flowering after about two weeks of intensive vegetation in order to save space. You brought to my attention the importance of balance and how that balance becomes less manageable in a more concentrated environment, so thank you.

jiji didn't say the roots barely touch. it's the medium. by this I guess jiji means the hydroton pebbles or such. you can still dwc, in fact I recommend it. for many small plants in a small space, you'll probably have to scrog. to make seeds you'll need a male if you want to seed it naturally. you're going to need pollen. if your first plant is a female, there's nothing wrong with cloning. my advice is, don't worry so much about yield. this will be no problem when you get a good grow going. worry more about how to do it than the outcome.

Polish, thanks for the advice. I was thinking for my first grow I'll use feminized seeds because I think correctly pollinating a plant would be a little bit to much for my first grow. But yeah you are totally right about not focusing on the result but rather on the grow I guess that is kinda true for anything, it is just exciting to think about yields. lol