LED may be easier to setup, handle, cheaper, etc, but it's debatable whether it matches the resin production and density of the flowers under HPS. Both have their pros and cons, but led is more noob friendly. But since u want to run a 250 watt this is what I recommend you do step by step:
First hang a carbon filter from the ceiling inside your tent. 4"x12" is the right size for that tent.
http://www.amazon.com/Phresh-Filter-701003-Minute-12-Inch/dp/B007ZU6IUY/
Then with 4" vent ducting connect the filter to a reflector/ballast combo. Your going to need a bulb (which u have), connected inside the reflector.
http://www.amazon.com/Hydrofarm-SBE250-250-Watt-Sunburst-E-Ballast/dp/B0038VG890/
The reflector connects to an inline fan, 190cfm:
http://www.amazon.com/VenTech-IF4-Inline-Duct-Fan/dp/B005KMOJPK/
The inline fan pulls air through the carbon filter, through the reflector so it cools the bulb, then blows the hot air outside the tent. From there some more vent ducting can lead the air outside or into the wall.
This what's required of you to set up an odor scrubbing vent system and air cooled hid system.
Option #2 LED
Buy this (never used it but some one here do) as its more affordable. That led light is slightly weaker than your hps but it's easier to set up and is cooler. It says 400w but only uses about half that.
http://www.topledgrowlight.com/mars-ii-led-grow-light-400w.html#.VAstkfmwKqY
You're still going to need the inline fan and carbon air filter. But you save on the ballast,reflector, and never have to buy a bulb again.
Personally I run only 180w LED and yield 3-4oz every 3 months from three plants. Here's a couple pics to show you the basic LED setup with vent sys I run. Same size tent as you too.
To answer these questions
1. hanging from the ceiling
2. yes, 1 inline fan, 1 carbon air filter
3.yes one 6" fan with clip is my recommendation
4.any more questions bro just holla
