Tips on kit - DR120

I am going to buy a DR120 in the UK.
What extractor fans should i be looking to get? I have a 250W HPS and high temperatures are not such a problem.

i have been growing in a closet and feel it's time for an upgrade.
i haven't controlled humidity before, so i am looking to get one of those temperature and humidity monitors?
any way i can hook up things to run automatically by themselves? e.g. maintain temps at 75degrees F? maintain humidity at 50%? so the extractor fan kicks in only when necessary?

i have seen rhino pro filters? is this what i should be getting?
are there different powers of these filters? do they last long or need to be replaced? do they consume huge amounts of electricity?
Fan & Filter Deals - Green's Horticulture
this is the website- they sell 3 diff types of fans and ducting, but i don't understand the difference.

any tips appreciated!!

Bump. Anyone, thoughts on what rhino fan to get for a 1.2,1.2,2m tent?
400w HPS, not 250w as I said before.

I've run anywhere from 400 to 1400 watts in a DR120. I'm using a 6 inch centrifugal with a speed controller to adjust flow. If you go with a 6 inch size it'll be more than enough for a 400. Not knowing your ambient temp, I hesitate to recommend anything smaller. I'm in USA and not familiar with the brands you mention. Better to buy a little over=sized, it'll give you options for more wattage should you decide to go that route.
HTH