inline fans are crap mate
Here get this
http://www.ebay.co.uk/itm/350622443453?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649
You`ll also want a filter go with atleast a 600mm long one but you may be better off splashing out on the next size up, buddy make good budget filters Rhino make the "best" filters
That fan is pretty good but if you have more cash RUCK make really good fans but they will cost over £100
That fan with a decent 6" carbon filter should pull more then enough air to keep your light cool hell it should be able to handle 2 600w hps`s in cool tubes easy as long as you have a filter with enough flow rate for it.
I`d go filter, cool tube then fan at the end but you could go cool tube, fan then filter but you filter won`t last as long as it won`t be protected by the pre filter but saying that keeping your filter outside the grow can keep it away from moister and heat both of these things can also shorten the life of your filter.