Beginner's questions - regarding CO2

Hello! I am a beginner's beginner, I got a 90 gallon tank from my friend and
want to set up a planted tank with lots of neons...(look like will be
pretty...)

Anyway, I am getting some easy-grow/medium-easy-grow plants, but after
viewing some articles, I found out that I might need to support CO2. I have
a 220W Jalli light and a canister filter.

I want to ask :

1. What CO2 system should be better for me in this situation? I found
several CO2 SOLENOID DIAPHRAGM VALVE on ebay, sould I need to buy one of
them?

2. If I really need those valves, shoud I also purchase a CO2 tank? Where
could I purchase them, and where could I refill them if they are empty?

3.Even though if I have them all, how can I know the plant got them? I
mean, does the CO2 automacilly go into water???

4. Do I really can turn off the CO2 at night?

5. Would the Co2 affect neons? Or could you recommand some article about
CO2 and fishes?

Thanks a lot! Any information will be helpful!

Doreen