Marine tanks are so complex its hard to give general advice.
Just looking at the pic of your tank it looks like you have aqualina lighting? Does it have 4 tubes? If so I'd recommend 3 blues (true actinic) and 1 white. (10 000k is probably best but so long as its above 6500k you'll be ok). This will give you the best colour IMO, and having a high blue spectrum will give you better penetration in the water (blue light penetrates deeper than any other colour).
You should be able to keep 80% of the corals you find in aquariums under those lighting conditions, you'll just have to play with photoperiod depending on the external conditions (ambient lighting etc).
I would recomend trying to focus on soft corals as they are easier as a rule. If you like hards, Euphilia's are probably the easiest to begin with. If you mix, make sure you use a good quality chemical filter such as Bio Chem Zorb, Purigen or good carbon and replace it regularly. This will pull out alot of the toxins that the corals will throw at each other through the water to try and kill each other.
Also, I'd recomend getting rid of your tusk fish for 2 reasons.
Firstly, not compatible with the mandarin you want, and if your looking at clowns, pick one of the red species to be safer.
Secondly, your live rock looks really good quality. Most people kill live rock not by bad water, but by keeping species of fish that scavenge and feed off the live rock. This sounds good in theory, but most of the time the fish clean off the "live" aspects of the rock, so you are left with just rock.
Seeing as you are running your tank on a cannister filter and UGF system, I'd really recomend doing as much as possible to keep your live rock in good nick. Careful fish selection is crucial in doing this. (Watch the angels too, but the yelllow tang would be fine after 6 to 12months of allowing the live rock to flourish, added too early, they too will clean off the live aspects of the rock).