Hello i want to lower my outback a little bit and i feel like a legacy suspension would be good.  Would it fit in my car and should i get a new or used set?  

Yes, it will bolt right in. If you are looking at used, make sure they're lower mileage or if they have higher miles, swap in a new set of struts. If you have an H6 engine, you will want to use the Outback springs in combination with the Legacy struts. The front springs are stiffer to accommodate the heavier engine.