I want to lower my fusion but not sure if it'll work with the system's weight. I don't know anything about suspensions but if the weight of my system is already lowering the rear of my car will a lowering kit lower it even more and cause rubbing or bottoming out?

Here's the lowering springs by steeda. http://www.steedafusion.com/parts/steeda-ford-fusion-lowering-springs-555-8306/

Every application is different, in my case I have an 03 impreza with 18in wheel. I had a 3in gap in the wheel well. I installed h&r lowering kit with 2in drop In the rear and about 500lbs in the rear it gave me three in lower. Theres about 2 cm between tire and wheel well but bucause of the spring rate it never tonches! Even with 3 passengers I'm safe.

You should also look into some shocks,swaybar made for lowering car help alot in the long run.

Yea, if you can find any...  

 

As of recently, ALL manufactures stopped making shocks for the Scion xb and rumor has it they are about to stop making them for all scions period.. 

 

Going to start having to go completely custom everything from here on out.

I'll have to measure and see what the gap is and how far it goes down from the weight