Alright dude whats up, I am going to help you with your problems since I only grow in soil and I am pretty damn good at it.
Watering, ok since your using soil with nutrients in it, it's going to be a little tougher for a new grower to know when the right time is to feed. Well basically the nutes in the soil will last about 3-4 with good growth plants that are feeding well. If I was vegging for 3-4 weeks my plants would be any where from 10-16 inches and very bushy. It really depends on when to feed, if you see yellowing in your leaves then that is a good sign they are hungry. That's normally what I went by when I first started in MG soil, for your next grow I would do fox farm ocean forest, very very good soil. Just watch your plants and listen, they speak to you ( i know i sound crazy ) but for real they will let you kno, you just have to pay close attention
Now on to when you should water and how much.
Well you should water when your pots feel light or if the soil feels dry, Gently rub or push your finger into the soil, if it's dry and dosen't stick to your finger your plants need water. I normally go by weight of pot because I am so familiar with how much they should weigh after water and how much when dry from lifting them so much. I use both methods and never have problems. Another way to tell if your plants need water is if your leaves are droopy, but be careful cause this could also mean they are overwatered. Once again to determine followering the other two methods.
Now for how much water you should be giving, I normally wait until I have drainge out of the bottom of the pot, but some soils hold moisutre really good and don't drain as fast. The way I truly learned was ALWAYS GIVE LESS!. Alot of people think more water is better and they'll get more nutes and grow bigeer. Tottally false biggest problem people have is over watering, If you think your giving them the right amount always give a little less then that, you'll never overwater then and you'll have much better results.
I sub'd and if you have any more questions pm or stop by my grow journal just search " multi strain grow "
Sorry if some of it's confusing hard for me to put things into words I like to show poeple when I teach But I am sure you should have a little better understanding now.
Good luck