Just take your time, don't spend $ if you don't have to. You can look on ebay aswell.
Taking another week to figure things out first will save you months later. The process will take 3 months min. seed to veg 3-7days min. veg-3 weeks, flower 6-12 weeks( this is not set in stone)
It took me 2 months to really look at what I needed vs. what I thought I needed.
Ask your self: how many will I have veg at one time, how many will have flow at one time. Look at the space that you have to use then take the time and read what lights work well with what the area you have. The light setups is a costly part of the process but it will be worth its weight in green in the long run. If you think that you will be able to get 6oz dry from two plants then they will need all the right factors to get that outcome.
If you are going to buy a hps system you will get alot of heat from a 400/600 you will need fresh air in and old air out, so you will need exhaust. and intake fans.
Your best bet is to start reading the Journals and the GrowF&Q then make your choice.
Hope this helped
GLG