This may be a noob question.. but would a sedan's rear suspension fit on a wagon?

No rear is completely different.

how about the lowered springs all around?

Fronts will work, rears will not.

To confirm, i have a KE Wagon, and are the front springs the same between a sedan and wagon? And the rear springs are completely different between wagon and sedan?

Front springs should interchange, but the rear ends are completely different.
When you have a chance, dive into the workshop manual and see for yourself.

The fronts are the same. The rears on sedans are IRS setup whereas the wagons are live beam axel.