First grow, here are my stats:
Soil (as is without my compost) mainly loamy with some sand
Seeds: early skunk by sensi seeds (not autoflowering)
Country: UK
Climate: generally wet, but coming into drier summer
Ph: roughly 6/7
Current status: 3 week old seedlings, rougly 4 inches tall, growing on a windowsill with moderate light, and a fan blowing over plants for a few hours per day. I just repotted all my plants into individual pots, as I had 4 plants in a shallow basin and was told this bad form, and isnt good. Made myself feel stupid over that, it's so obvious. Also I'm still figuring out an over/under watering issue. Trying to diagnose and it's hard to tell for a newbie such as myself.

List of products I have around that may be helpful?
Big bag of vermiculite
John jnes ericaceous compost
Perlite
Bone meal
Fish blood and bone
Multi purpose compost (verve) 60% peat for "not acidic plants"
Tomato feed (loads of it)

Right, hi!
First grow is going well, I'm on track to get my plants outside this week and i think most of them are ready for it. I am mixing up my soil for the holes (advice on how deep and wide please) and have 3 big sacks of good compost (75l each). I am thinking about getting some worm castings, (how much?) And adding another nitrogen rich fert to the soil, what should this be? I will also add 30% perlite and I hear that vermiculite does some good stuff, can someone explain that please? Also, should I add my blood and bone to it? Finally I will mix in some bone meal.
Sound good? Any advice?