Well, that's not really a system specific question, more a general hydroponics one but I'll go in anyway.
IWS is the same system by another manufacturer. I pot based flood and drain with a brain and float valves etc.
Your PPM shouldn't be any specific number. It's not a be all and end all, you just use it to keep an eye on what your plants are doing. If it goes up over time, they are drinking more than feeding and vice versa. A good rule of thumb is to take whatever dosage your nutrients say on the bottle and half it or quarter it to start with.
7 times a day on a 24hr or an 18 hour day? I guess 24 which is every three hours which seems fine. What is the problem?
As a rough estimate. Your plants once they are in veg, maybe 8 inches tall with 4 sets of leaves, anywhere between 400-800. You can go up to 1500 in flower, but more isn't always more.