Do you need to use calmag with ro water?
-Yes. RO water doesnt contain cal/mag. Most 3 part nutrient lines cover this for basics though. You can always add if needed on top of a 3 part nute line.
Is 300-400 ppm OK for 7 inch plant , early stage of veg?
Since you are using RO water, this means that ppm number is all from your additions(nutes/cal/mag boost etc.)
If you have good roots established and 4-5 nodes then it should be good at that ppm. If the leaf tips begin to yellow...dial the nutes back.
How to fix clawing at the tips of plant?
Clawing is usually one result of too much N and is usually seen along with dark green leaves. Be sure not to mistake wilt or droop for "claw".
Cut back on the nitrogen (grow/veg nutrient)
Do I leave my pump and chiller running at night or can i shut it off until lights on?
I dont have much experience in this area since I'm not a summer time grower, but would imagine it to be controlled by a thermostat?
It should cut off when the desired temp is reached. Not sure what kind of chiller you have so....
When plants drink up water and nutes, do I top with plain water or water and nutes?
You have to monitor how much nutrient it is taking up with the water. If it isnt taking up nutrients with the water(which is evident in ppm spikes) then you dont want to add back anything but water since thats all the plant is using.
If I top with nutes and water how do I raise it just a little, do I add more poms then original or less?
This goes with the last question as well. If the plants are calling for more nutrients and water, then you mix just what was taken by figuring out your measurements per gallon and how many gallons are used from the res that you will be replacing.