Rather than building a GPU rig for altcoins, I would suggest you directly jump over the next stage, scrypt ASIC. GPU mining of most altcoins is going to be out the door in a few weeks. If I were you with some decent money, I'd order a KNC Titan scrypt ASIC or Fibonacci chips and start mining Litecoins when I receive it. Meanwhile you can do the buy-sell trading. And if you have a couple of GPUs you want to utilize right now, point them to some X11 coins such as DarkCoin.