So u had the bi-color for a month before it died.... or u had a few of the damsels for a month, added one more the 5th week and then got the bi-color in the 6th week which your in now??
It is highly recommended that you should QT. I suggest and recommended it (although I personally don't). Its risky, you can introduce pests and diseases into your tank and you cannot treat many of them inside your tank (if doing a reef), so IF you picked ur something nasty you would need one anyways. Also, by QTing you greatly reduce your odds of introducing any of these into your display.
IMO, a qt is no different then a display in the fact that you want to go as big as you can afford and have room for... also depends alot on the types of fish you plan to keep and quantity even IMO (never know something could happen and you need to get all your fish out and to safety quick, like kid over feeding and spiking levels for instance). Im not saying go buy another 110, but if you have the room maybe do a 50 breeder or something instead of a 10-20g that could leave your fish cramped and stressed in a quick move, especially since your planning on doing a couple tangs.
Not having a skimmer in the beginning isn't a huge deal IMO, and I doubt that had anything to do with the bi-colors death.... however possibly (small possibility, but possible) if you didnt clean the skimmer and it was brand new there may have been some kind of chemicals from the building process that may have gotten into the water and played a role. I don't know a ton as far as building w/ acrylic and the possibility of any of the bonding chemicals doing any damage, but I know new silicone has been known to cause issues and be a killer. I had a friend who used pure silicone and still wiped out his tank when he built a new sump for his larger skimmer and didn't rinse it out well after letting it cure for 24 hrs before putting it online!
I think your stocking plans are doable, depending on what tangs your thinking of adding. If you do a Zebrasoma (ie. yellow, purple.... stay away from sailfin's tho) and a Ctenochaetus ( ie. bristletooth, kole) you would probably be ok, although a 6'+ tank would be best and prefered for any tang IMO long term.
Also, a 28" deep tank, you may actually want to consider looking at MH, supplemented by t5's..... If I remember right there was a study and t5's do not penetrate below 20-24" If your 100% sure u only ever want softies and one frogspawn I wouldn't go dropping a ton of $ on a light..... if nothing else and u like your canopy, buy a DIY kit, they are pretty easy to set up if your not afraid of playing with electricity and water.
