Starting Hydro

So, I am converting my entire setup to move past soil, and on to hydroponics. I decided on using an ebb and flow system, most of which I will be building myself. However, I have a few questions since I am new to this.

Can I just get a PH meter or do I have to get a PPM meter also? How good of a PH meter?

What nutrients do you recommend? I was going to use either Flora Nova, or Sensei Nutrients. Do you just use the veg nutrient during veg cycle and the flowering nutrient during flowering cycle or do you combine them? When do you start adding nutrients usually?

I plan on getting a 20 gal res for three 36" trays of about 3 plants each. What kind of pump should I get?

get both ph and ppm. sometimes they come together.
buy liquid ph down.
i'd go with flora nova
just follow the directions on the bottle.
it depends how far through a tube will that water be moving.

I was thinking about using 3x 1/2" drip lines, with three 1/4" lines coming off those running drip stakes into rockwool cubes sitting on rockwool sheets.

I was thinking about this one... just the 200gph one but I dont know shit about if its enough.
Discount Hydroponics - Rio Pumps

Also, how many times a day should I run the solution? I was thinking something like 3-5 times a day for 5 minutes depending on plant size. Or will the nutrient tell me how often I need to add it also?