So I currently have a 3" lift with Bilstein 5100.
I want to go 4.5" with some 32s.

If possible I want to keep my shocks which is for a 2-3" lift.
When I installed the shocks I had to compress them to fit.

If I keep my current shocks whats the highest I could go so they still function and have length to absorb shocks?

Could I go 3.5" lift? If I want higher I guess I need new shocks?

 

If you add an inch of lift, your dampers will limit your flex big time. They might not even work. You should get new shocks.

Also, the best way to determine what shock length you'll need is to install the springs without shocks, flex it and measure.