is antminer S9 or asic hardware pretty much the only viable option for profit mining these day's?
for a custom built rig does CPU matter (# of cores) or would focusing on GPU be best?
I'd say GPU is a winner against aisic. The reason is that when your asic will get obsolete (and it happens very quick) you will have very narrow range to choose what to mine next and you will not be able to sell it in the market, so you will scrap it. While GPU's are very easy to sell to gamers, and you can choose within a very wide range of mining coins