What can you put in after the cycle (right after)

[SeaSerpant]

Hey everyone,
I have talked about starting a tank for almost 2 years now! But now i have! It is a nice 20g set up and is right now in the process of clearing the water from all the sand junk!

Now to the point! After the 3 week cycle you put in your cuc, are you able to put in any fish or corals yet. The people at my lfs (very nice knowledgable people) said that there are a few corals that you can put in but first you put in cuc after three weeks, they said you can put in pulsing xenia and one other, and then wait 3 weeks for fish and another 3 weeks for full on coral.

Is this right?

Thanks
SeaSerpant

P.S
Is there anything that you can put in your filter to filter out the sand just and then just chuck out? like cloth or something?