Cheers mate! I'm probably not the best person to ask as I'm a beginner too. This is only my second grow. I mix up 5 litres of water at a time because then I can more accurately measure out the nutes in the right ratio. I don't necessarily use all that 5 litres. After a week, I tip away what hasn't been used, which is most of it, and mix some up fresh.
Watering and how much to water has always been a fuzzy topic for me too. A popular opinion is to water until you get "run off" i.e. the water starts coming out the bottom of the pot. I guess that largely depends on what stage the plant is in its life and how much water it can take on and absorb. For me right now, I've been watering it until I've got a nice pool of water form at the top and I just allow it to sink back down, which it does within 2-3 seconds. No run off. I do this every other day because my RH is between 50 and 60% and a day isn't enough for the soil to adequately dry out from the previous feeding. Whatever it is I'm doing the plant seems to like it.
I don't think there's any hard, fast rule about watering. It largely depends on the individual setup, the conditions, the strain and the stage in its life cycle. I think it's one of those things that you get a feel for the more experienced you get. I'm not there yet and I will make mistakes. lol!
Good luck with it bro!