600w + mylar productions trying to get under-and-away need some help

hello i am just in need of some quick guidance on mediums, soils.(although i think my system is hydroponic) and nutrients to grow my plants from seeds.
so.. here's what's going on..

i have bought off ebay, the atami wilma 8 pot system+the 1.2mx1.2mx2m mylar tents with ONE 600w lamp, i am planning to pop to my local seed store and get some seeds, since i have bought a hydroponics(?) system. for every gallon of water i put into the "resevoir" what else do i need to apply? and whats the best stuff? is it fox farm? however take into consideration i am from the uk, so the products can be bought on the net. ebay only unless its a .co.uk store, and i don't want a product that has £30 postage lol
and how many plants should i grow in my 8 pot atami system with 1 600w lamp, i can have less than 8 or more with a few soil grows, if need be i can even buy another lamp..?
what do i do!

well i just googled the wilma and its a hydroponic setup looks like "drain to res" i would use either hydroton "clay pebbles" or coco. u only want 1 plant per pot so i would make sure u buy feminised seeds.that wilma 8 pot system isnt build for soil.pickup a 2 part nutrient sulotion and it will tell u on the package what to add per gallon.your light is good u shouldnt need another light unless u wanna add more plants but even then u will need a bigger tent , your kinda pushing 8 plants in that tent to depending on how big u want them. GL

thanks very much. this will be first ever grow, not just marijuana wise, but i haven't even grown tomatoes, haha :/
but still :C
do you think it is a good idea to use hydroponics system for first time?
The system loooks simple, and i thought coco, was a soil.
would it be best to use, the clay pebbles you said then get two nutrients, and the nutrients you put on the pebbles or into the bath which auto feeds the plants??
thanks very much