using 20gal to kickstart 120gal

[big_money]

We purchased a used 120 gallon tank and have not set it up yet. I'm still building the stand and we want to paint our living room before we start this tank. The 120 gallon tank has some bioballs (it's a "uniquarium" brand acrylic tank), and I'm also creating my own DIY base rock (portland cement, coral sand & crushed oyster shells/crushed coral -- soaking for 5-6 weeks until the ph drops).
While we're waiting we purchased a 1+ year old, 20 gallon tank that has two small fish (a green and a blue chromis) a sea urchin and a starfish we've named "cinco". The 20 gallon tank has a DSB and alot (20+ pounds?) of LR. I tested the water and was pleasantly surprised to see the nitrates at zero! (I guess the LR and DSB are removing all the nitrates?)
What would be the best way to use the 20 gallon tank to reduce the cycle time of the 120 gallon tank?
We want the 120 gallon tank to be a FOWLR for the foreseeable future. We're probably looking at 2-3 weeks before we start the 120 gallon tank.

 

[hot883]

You can set up the 120 and then seed the sand from the 20 and the lr as well adding it to the new tank. Still will have to wait a couple of weeks before adding fish though IMO.

 

[big_money]

How much LR and LS should I take out of the 20 to seed the 120? all? some?
Do I run the risk of disrupting the 20 when I remove some of the LR and LS? Will I potentially release some nitrates from the DSB? (can I just compensate for that with some water changes?) I'd really like to not kill any of the fish or inverts.
Can I start "seeding" some of my bioballs from my 120 over the next 2-3 weeks to help with shortening the cycle time? The 20 is pretty full at this point, so I was thinking of some sort of DIY temporary "addition" onto the 20 (increasing the total water volume of the 20 -- enough to hold maybe 25% of the bioballs from the 120).
Or could I remove some of the LR right now and add the bioballs directly into the 20? If so, how much and how would I keep the LR I have removed alive for the next 2-3 weeks? (in some sort of rubbermaid tub with salt water and something to move the water around?)