please don't go to b&q for your soil bro and do NOT get the bio bizz all mix, it is far too hot for autos and will stunt their early growth or even kill them!! if you are in the uk go for plagron light mix, thats the soil i have used my previous two grows and i wouldn't use anything else, you could go for the biobizz light mix also, if you are going with HPS i wouldn't go any bigger than a 250W light or your temps will be through the roof in that size of room,if you go on ebay you can get a 4" RVK extraction fan and rhino pro carbon filter for around £100 that will deal with the smell and help remove the stale air out of your cab, i would also recommend getting a good ph pen