I would take some of the substrate and plants from the 120g planted tank, put it into the new tank, and some filter media from the 120g filter and put it into the new filter. The whole purpose of cycling is to build up the 2 kinds of beneficial bacteria on the new filter, gravel, etc. If you already have those things from a fully established tank, it can happen pretty quick. Even if you don't want to use the substrate from the old tank in the new one, then put it into a mesh bag inside the tank near the filter intake or something just to get the bacteria into the new filter. Adding water from a established tank does nothing, despite people saying they do it, the bacteria we need colonizes on surfaces, its not free floating. That's why plants, gravel and filter material from an established tank can almost instantly start up a new tank.
What kind of shrimp are you moving into there? The only thing transferring water over, is that it may help the shrimp if they are a sensitive shrimp that like "old water". Then you do a 50/50 mix of old water and new water, just so the new water has some of the micro-organism life that the shrimp like.