Soon starting :D Help!

Good day everyone!
so I am close to start growing some plants, decided for soil (aimed for 3 in 80/80/160box) with a nice dual Led panel.
I will be using 3x 20l bucket drilled into pots filled with Plagron LightMix, and for early seedling Canna Terra Seed
Mix, not sure if I should buy some of more perlite to add, should I ?

Gonna be using Tap water and maybe some bottled water that has cal / mag inside, the thing is should I go for bottle of cal/mag+ ? or there is 100% no need for that, The RO will be in future but not yet.
The ppm of city water is around 300

When feeding with nutirents should be started ? I guess after secound pair of leaves, or 3rd ?
Also I am planing to make only Uncles Ben toping metode to make it as simple as I possible, can I get some more info from you about it, how efective it is and how to exacly go for it.

Cheers.

I would make use of any advice so also feel free to suggest anything and point me out if I have forgotten something and if I am on a good way to go or not !

read these http://www.growweedeasy.com/basics and http://www.ilovegrowingmarijuana.com/guides

with 300ppm tap, you shouldnt need any cal mag. with the ferts included in your soil, i wouldnt feed until at least 4-5 nodes and then at 1/4 strength for a week, then 1/2 for a week then full strength, water every second.

Hey yeah the soil with fertilizer in it will sustain them for 3 to 4 weeks with out anything extra. Dont feed anything until at least 4-5 nodes like Growdict says. You will need to decide how many colas you want in choosing wheather to top for 4 or 6 colas, keep in mind some lower branching will end up being tops too. So if you top keep in mind which branches will be tops too. So if you top for 4 colas plus you have 2 good main branch shoots you have 6 top colas, top again for 12 in veg and give them a few weeks and flip. MD

Thanks both of you, very helpful, so Im not buying cal mag as its not needed yet, and Yeah, I wish Im not going to fail at toping, lol, 6 - 12 tops !! I was thinking that, if I will make just 4 good tops after their first topping I will be fine

I'd get at least small bottle of calmag. Better to have and not need it than the other way around. My city water averages 260-320ppm and I needed calmag @ week 3. You increase your possible need for it with LEDs from everything I've seen. I just started switching over.

Good luck!