1st time grower

forget the 20-20-20. Get a good hydro line of nutes, I like GH. Check out Lucas formula, it's cheap and easy. Dont skimp on lighting. A good socket, bulb, ballast and air cooled hood is goona cost 300-400 so be prepared to spend more than the 400 you were thinking. A chiller for the rez should also be used. You're also going to need a fan for the air cooled hood, 6" with at least 400cfm (the filter needs to be 6", recommend a phresh brand). The 4" duct and fan is for intake. You can use a smaller size ro filter to save some dough, it will just run slower.

 

Seedlings won't need any nutrients for some time.  Lucas formula is one bottle of nutrients for all stages of plant growth.   It's simple, and very effective.  It's the best way to learn hydroponics.
 
On that note, check out a Hempy bucket, as your first method of hyrdoponics, and try Lucas as your first nutrient regime.  It's tough to go wrong in that regard.

 

what hydro system are you planning to use? for first timers I would recommend DWC or one of its variants.
 
I would use proper cannabis aimed hydro nutes.
why use reverse osmosis water? what's wrong with your tap water?
give your seedlings regular veg nutes, in the correct strength obviosly.
 
what's fiskers?
what's rw?
 
I'm not sure what a PH and ppm kit is, just get some cheap digital meters. I use the £10 Chinese ones and they work perfectly well and last many years. 
 
your  total spend sounds ridiculous. you don't need to spend that sort of cash.
 
what size is your grow area?

 

DWC is a nice and simple place to start, but make sure you have enough air going through the system. more air = more bud. I recommend no less than 10L/m per 5 gallon bucket

my tap water is 0.1 so I guess yours is quite a bit stronger, but are you sure you need it? it's quite expensive

don't add nutes like that, use an EC or ppm meter and do it properly. having the EC exactly how the plants want it makes a huge difference. the meter will tell you exactly what the plants require, you just need to match it.

use the smallest piece of rockwool you can get away with. that stuff holds way too much water

your better off just buying a cheap Chinese £10 EC and PH meters, they are easy to use, cheap and last for years. their accuracy is way more than you need.

that's a nice size grow area for a 600w I would probably have 9x 5gallon buckets in there

 

some of this is fact, and some of this is my opinion..

one of those pumps per bucket will do ok, more air = more bud, but dropping to 7L/m is certainly not going to harm the plant

if I were you I would buy the water and mix it with your tap water until you see an EC of 0.2, that won't harm your plant at all and it will save you buying so much water.

I would do that for the first grow and then switch to tap water for the second, if you see any problems just top up your tank with the store bought water.

test your nutrient solution every day. if the strength rises its too strong. if the strength falls, it's too weak.
the idea is to get the water and dissolved solids the same ratio as the plant is currently using. that's the goldgrower method. it works for me, I never get any nutrient issues be it under or over fertilised

I would cut a 1cm cube of rockwool and use that to germinate each seed. you can put it in the system right away then and it gets more air and grows faster.

ScrOG is a great way to maximize the usage of the light. with a 600w lamp there's probably not that much need to go to the trouble as it has so much penetration of good light. for smaller grows it makes a big difference though

I wouldn't bother with led, they are total rubbish compared to hps watt for watt or cost for cost. if you want to up the lighting I suggest buying a dimmable 600 watt hps now, and when you want to add more light buy another 600w dimmable hps. you can then run both on 400watts giving you 800watts and you will have a far far better result compared to adding 200w of led. you can then have both running on 600 if your ventilation can handle it.

if your reason of adding dry ice is to add co2, in my experience adding co2 only makes a difference if you have everything else spot on and even then your far better off using co2 from a bottle or fire extinguisher. using dry ice isn't worth bothering with. when using co2 you need to have cool tubes so you can close all other ventilation while adding it. otherwise it will get sucked out straight away. your better off spending your money on a bigger exhaust fan and better circulatory fans. this will give you plenty of co2

 

I think a 4" fan maybe ok but to be sure I would use a 6" fan to draw air out and a 4-5" bringing air in.

the 4" exhaust may be ok if it has no ducting and no filter to move air through

 

I have no idea what that is but in my 20+ years of experience to get any benefit from any of these "magic" potions you need to have everything spot on, and I really do mean spot on. even now after countless successful grows rarely do I get everything spot on. it's hard to give the plants enough light to the leaves and oxygen to the roots.

my advice is to keep things simple, get one nutrient program and practice getting it right a few times. getting your nutes in balance will give you far more extra bud than any booster

 

if you sprayed the plants with liquid co2 it would freeze them. I don't understand what you mean. do you have a link to this product for sale? adding co2 in its gas state is only useful if you have the plants metabolism running very fast. it's really not something worth concerning yourself about. learn to get your nutes balanced, light fully utilized and get as much oxygen to the roots as possible. if you get all this right then adding co2 can help. but then you will have to change your ventilation set up to quite a degree. in my opinion your better off adding more light if you ever get to that stage

 

thanks for the link. it looks like they have mixed some nutes in with carbonated water. in my opinion totally pointless as wetting the stomata (breathing holes) stops gaseous exchange. plus spraying the water will release the co2 pretty much straight away. and as far as the nutrients go, if you have your nutes correctly balanced then adding more via spray (if it's even possible for the plant to utilise it) will actually overdose the plant...
 
sorry about the rant, there are so many products out there with empty promises using marketing patter to target newbies that just don't know any better