Ive been reading and watching youtube from other JK owners. im not sure if i need to replace my shocks/springs when im lifting my JKU. I plan to do some mudding and some low level trails in my off time. I recently had my oil changed and the mechanic showed me remnants of fluid coming out of my stock shocks. is that normal? otherwise id just get extenders for the shocks. My goal is to get 35" tires with 18" wheels or can i get away with 20" wheels?
You could technically do a spacer lift which would keep your stock springs and add spacers, but you'd still need to add longer shocks, there's no way around that. Still, if you're going through that effort, replacing the springs with longer springs will be the preferable way to lift it to 2.5", whether you're planning on doing on-road, off-road, or both.
Fluid shouldn't be coming out of your shocks, no. That means they are probably slowly leaking.
With 35s you need 4" of lift or more, not 2". 2" of lift is simply not enough for 35s. You'll lose up-travel, which will make your ride quality worse both on-road, and especially off-road.
You can run 20" wheels and a 35" tire with a 4" lift. However, a 20" wheel is going to be a bad idea if you plan on doing any real off-roading. You'll want more sidewall on your tire if you're actually going to off-road it, and a 20" is going to be closer to rubber band tires (think Pimp My Ride).