So after years of buying equipment and saying we want a reef setup, we finally did it!

We started cycling our 90 gallon setup a few weeks ago with lots of "dead" live rock and substrate. After two days, our tank (which was used) cracked along the back. My 11 year old son and I transplanted all the rock and most of the water into big plastic totes and we ordered the brand new 120 gallon reef ready tank to replace it. Our tank has been running about two and a half weeks now (a week of that in tubs with power heads) and we are nearing the end of the cycling process! Here is the total set up:

120 gallon display
55 gallon sump with refuguim built in
LED ZEAL lights
ehime pump
ehime heater
and lots of live rock

we plan on adding an auto topoff eventually as we have lots of room left under the stand.

so here is my first question...

when end should I add my cuc?
Ive seen some people say as soon as algae begins growing and others say wait till the cycle is done...
i have a diatom bloom already
my ammonia is 0
my nitrites are about .25
and my nitrates are Around 80 (they were over 160, but after a water change they are back down a bit)

I would like like to go on Friday if I can, but I don't mind waiting if I need to.

Also would it be detrimental to get a couple hardy fish when I get my cuc?

thanks in advance.