It is very good that you are so receptive to advice and constructive criticism.
The problem is is that asking a forum for advice is not proper research, IMHO. It's asking people for advice, which can work out great, as in this case, but can also be disasterous. What if you didn't get an AndyWatson, a Donya, or me responding to this thread? How do you know what we are saying is true? You're trusting that we did the research and reading before hand and we did, but you need to go and do this reading for yourself.
Because I have done reading, I have caught people giving poor advice in other forums, or their advice is incomplete. Your questions also change. They become more specific. What books have your actually read?
As for a CUC, it's usually comprised of a group of snails, crabs, and shrimp that serve different functions in a tank. Some clean up waste and food products, others eat algae, others sift the substrate, others focus on the glass and other surfaces. A good CUC will have all these bases covered and will have interesting habits. I love my CUCs, they are very interesting to watch. I agonized over their selection because I was also thinking about long term CUC survival. To me, these are not disposable organisms where once they do their job, they become unimportant. They can become long-standing members of a tank's stock list. I care about whether they are getting enough to eat, and if my tank is clean, I'll provide them with food.
Here's my 8g CUC
2 Electric blue hermits (almost didn't do these, remember Donya, but have not regretted my decision)
1 Emerald crab
1 banded trochus
1 Asterea snail
1 Nassarius snail (had two, a hermit killed one)
1 Fire shrimp
I may add another asterea and some ceriths from my 36g, but it's better to have to add CUC over time than to have too much CUC. Yes, you may sort out your algae problems faster, but you also are left with starving CUC.
This is what happens when I post after an all-nighter due to a nieghbor's car horn getting stuck on from midnight to 7am. 
