Hi mate,
I'm no expert on soils, but i always just use any cheap compost my garden centre has, i dont see the point of spending so much on the big brand soil companies. As long as the compost you get has some nutrients in it'll be fine. The only thing you need to worry about is drainage problems. You dont want the water clogging up in the soil and rotting the roots, to prevent this mix in some perlite which is basically sand. You will need some nutes for you plant the keep it growing and healthy, you can get some cheap nutes for tomato's from all garden centres. You can grow amazing quality weed with massive yields without spending loads on your setup..
Good luck mate, i hope to see a grow journal when you start growing !