Hey man, nice PC! First and foremost, you bought the kind of box that is the best. It's taller than it is wider, which allows your plant(s) to grow upwards, so you don't really have to worry about running out of space.
Lights: you could easily fit around four cfl bulbs inside. Some people for the vegetative phase buy lights that have a cold spectrum eg. 6500k but there are also growers that buy eg. three "cold" lights and one "warm" light (2700k). There have been amazing results utilizing both schools (I for one have three "cold" lights and one "warm") apparently it is good to mix up the light spectrum, but as I have said, the results at the end come down more or less the same. If you can get your hands on lets say, 4 cfl bulbs, each having 25W, then you have 100W of "power" which is fantastic. While it is important to look at the wattage, the most important thing are the lumens. I have four 23W bulbs that give out 1520 lumens each. 1520 [lumens] x 4 [bulbs] = 6080 [lumens] in total which is more than enough.
When your flower starts to... flower, then you want to have (all) or most of the bulbs in the "warm" spectrum for example: three 2700k bulbs and one 6500k (or all of them in the 2700k spectrum)
Soil: there are a lot of information regarding soil/nutrients and what not on the internet. 99% of growers state that "it all begins with the soil" so the better the quality of the soil, the better the results are going to be.
You know what mate, I made a PC grow box journal a month ago, but unfortunately it is dead now (because I was out of the house for a whole month). I am in the middle of a new PC grow atm, but I'll start a journal when I'll be 100% positive that I won't fuck up again by leaving my plant unattended. Go check it out, it should have all the details you need, I also made a lot of pictures/information during the process of building the box. You should also check out eatspam. He made a fantastic grow journal even more detailed than mine. If you read through those journals, then you should be able to build a box yourself in no time.
Of course if you will have any more questions do feel free to ask.
Good luck mate, greetings from Poland.
P.S. the link to my "dead" journal is in my signature.
