Skittles can't be Ink but he could be an Infiltrator. He's not all there to begin with so split personality caused by potential experimentation on him is possible. Skittles personality A could be aware of the B personality and try and prevent himself from infiltrating a stronghold/safehouse (He didn't let Angel and Kalani take him to the Tower). He isn't overly paranoid and definitely not schizophrenic, so he can't be Bill Roberts (he isn't homocidal violent).
The creatures are evolving whether by Kirby style consume and become or experimentation by Smart Ones has yet to be determined.
Also the probability that Bill Roberts is Ink is very high. The newscast said he was currently being transported to a mental help facility at the time of the outbreak. Kc can't make the series insanely difficult to follow (remember the complaints that Inception was too high brow for most) so mentioning Bill Roberts and not having him later in the plot would just be pointless.
On to the Big Ones super growth. With an increase in size that large testosterone levels would have to skyrocket. Funny thing about testosterone, if its level spikes so does the estrogen levels. They've yet to mention the massive bitch-tits on a behemoth (Thank you Fight Club) so I'm curious as to how they were made. But hey, the z-germ/virus could null and void the estrogen and utilize it on something else. Its SciFi, who cares if its possible it just is!
On the topic of them being made, can a Smart One control a Big One? It has been mentioned that the standard Biters leave them the hell alone. They have yet to be deployed in a tactical manner by any of the Smart Ones. Two controlled behemoths would have screwed The Tower over on so many levels... or maybe just the ground floor.
Well that's my two cents.