One Luci in the "nose" section of Colie, at least 3 (maybe even 4, or 5 if someone is skilled) could fit in it's main part, two into the engine section, and at least one in the rest. This gives us about 9 Lucy's, though I think that if somebody would break the L into very small parts and fill with them the Colie's hull, 12 Lucifers would fit in it. Though it would take quite some time to check it, frankly.
Well, the Colossus wasn't supossed to be a ship to fight new threats. As somebody already said it, the only problem laid in the drawing boards, where designers didn't think that the Shivans could bring, bigger, nastier ships than before.
Also, the only known fights involving Colossus and the Sathanas are really tacticless. Collie should have waited further into the system for the Sath, and warp in on its side, bring most of his firepower while avoiding Sathanis foward beams.
Oh, and why do you think that Volition gave the Lucy the SReds ? Maybe the GTVA's scientists were able to annalyze the beam pattern/whatever and produce far more effective armor, reducing the Luci's beams effectiveness dramatically ?