Changing Springs

I have noticed on my 2003 Celica that there is room between the rear tires and the tire well but cannot fit my hand straight in, it must come at an angle. The front left is the same way but the front right I can easily put my fist as clearance. I am in the process of changing the rear struts first as it seems cheaper overall compared to the front struts. After taking a closer look at my springs I am not 100% on it but I think there may be damage just because of the rust on them and how old they are and how most of the car is a certain height except for the front right. My question is what kind of springs can I put? I do not want anything fancy just to bring it as close to OEM as I can. What I dont understand is the drop that different springs give as I look at the different brands. When it says a 1.5" drop where is that measured? And what kind of springs came stock with the car? I would like to order the springs soon so that I can put them on the new struts I ordered instead of doing everything twice.