any seed will do.....for 4 plants get a 400watt HPS (you can grow the same number of plants with a 250watter but a 400 one will do the job better producing bigger buds and covering more sufficiently the same space)....
the HPS bulbs have a rated life of 10,000 hrs of continuous operation i think....anyway it is wiseable to change the bulbs every year more or less given the thought that you grow one crop start to finish twice a year...