A lot depends on the system, environment and the stage of growth.

Hey hex, sorry for the late reply.

I'm planning to use a simple water culture system.

How much water per plant would you recommend for green chili and tomato?

I am not so old at this myself but have run an outside dutch bucket system for three years, a summer deal. You will need at least a 2 gallon per plant system for tomatoes. In the summer months in my system the tomatoes have taken at times over a gallon per plant per day, (full fruit). I know that sounds like a lot, it is not. I suggest larger if you can. Right now I run 7 tomatoes plants and this year ended up using a smaller cooler (28 quart, had it on hand) for the solution and it is being depleted every day or so depending on temp and rain. Ran four or five tomato plants the last 2 years with a 48 quart cooler and did well. It is a pain this year but do get fresh solution quite regularly... lol. Hope this helps.

It will depend on the system as some (eg flood and drain) can lose as much water to evaporation as the plants are taking up ;) I have 8 toms with 6 trusses of fruit so far that are getting 1.5L of nutes each per day. They are in an outdoor high pressure aero chamber, run to waste so i can monitor how much is going in and coming out, along with the ppm and PH difference.Air temps have been warm for here 32C but that may seem pretty cool to some folks in warmer climates lol. If the plants are taking gallons a day its a good idea to reduce the nute strength to prevent a build up in the medium. Ideally, its worth comparing the inlet/outlet ppm/ph if you can..

It depends on how large you'd like them to grow (since the roots can grow quite large) and how often you'd be willing to water them. A popular thing I've seen for tomato's and peppers is to have 5 gallon buckets for each plant as a DWC system (deep water culture - the roots are submerged in the nutrient solution and a air bubbler pumps oxygen into the water). Smaller containers would work as well but would require more frequent topping up unless an automation system is set up Tomato's take up more water than non-flowering vegetables such as lettuce, which would only need about a liter of water, so probably 2 liters is the minimum.