Dont over think it, start it in a cup till its roots are everywhere then transplant into final pot. No biggy. Or just start in final pot, it dont really matter. If it was growing in nature it is essentually starting in a giant earth sized pot.
I use 8 gal smart pots in giant saucers to catch the water and any runoff I just let it sit in it and the plant eventually soaks it up or it evaperates. No need to raise it up off the saucer.
Growing in dirt I think your ph is fine, its not as critical when growing in dirt. Just make sure the soil you use drains real good. You can probably hold off on nutes for a while, they are still real small so they don't need much. 3 plants under 600watts shouldn't be to bad, I use two 600hps for 4 plants in a 4x4 room with good results.
Do you know what kind of seeds they are or are they just bag seed? 6 months is a long time to wait for some bull shit seeds so hopefully they are at least from a decent bag if they are just bag seed.
Look into making a cloner, one that uses the mini sprinkler heads in some pex pipe works real good. U can set it on a timer to come on for 15 min every 2 or 3 hours or so and do just fine. This will make life alot easier and open the door to perpetual growing.
For my cloner and clones I use a 150 watt hps untill they are ready to swap with the flowers that are finished. This makes for a harvest every 3 months or so since the clones are teken right before I switch to flowering.
Number one thing is to be PATIENT and dont over think it. growing weed is easy, dont fuck with them just because your bored.
