Ok here goes.First off i agree you should have a good soil,however i wouldnt buy any speciality brand because its just way overpriced.When i do soil grows i get a bail of peat moss from home depot a couple of bags of perlite.This comes out to be less in price compared to fox farms (20 dollars for peat at 3 cubic feet,perlite and 2 pots vs. 1 bag of fox farm at 18 dollars and is only 2 cubic feet) or any other speciality mix and you have plenty of peat moss left for other grows versus youll have to get a couple more bags of designer soil mixes.mix 60/40 peat/perlite.The peat moss is very airey and the perlite helps with the drainage.Also peat moss is a nuetral base which helps keep ph in your soil.Ive used this combo for years before i started an ebb and flow, dispite everyone telling me that I was going to get into trouble ( i.e. mold,fungus,) I actually found it quite pleasant to work with.Start off with small pots, one quart pots are good to start with,or in your case a good size dixey cup.Germinate your seeds first by soaking your seeds in a shot glass of water either till they sink or they start to crack the shells( i usually wait till they crack)plant them about 3/4 to an inch below the surface stick under your light and watch.
Secondly i have sprouted many plants under a 600 watt HPS,You dont need a screen to shade them and the light is not too much for them. just keep the light at about 3 feet and as they grow to the light slowely lower it.just watch for any kind of stress.if they start to stress raise the light back up. My theory behind this is that if you grow outside you dont start off puting them under floros then move them to the sun, No you put them in the ground right under the sun.Why not use the light source you are going to grow with from start to finish.And there will be no light stress going from a floro to an HID which can set you back a bit.
As for watering,when tou fill your pots with your new medium do the wieght test.Pick up the pot get a feel for the whieght of the pot with dry soil then water it.only water till liquid just starts to come out the bottom. Dont water till she feels light again.This works for all pot sizes.