You have some good options to choose from.
Even though this doesn't look like a deep WR class and he has a veteran QB returning, I would be hesitant to keep Nick Harwell from that group. WRs are the most volatile IMO.
Both Joseph Randle and Branden Oliver are solid RB1s. The big negative with Randle is they will be breaking in a new QB. You can look at this as a positive and a negative. But if OkSt struggles moving the chains, it ultimately decreases Randle's value. He's an NFL-caliber RB, so I'm not predicting any kind of doom and gloom, just looking at the slightest edge I can find.
With Oliver, great season, but Buffalo isn't exactly an offensive juggarnaut. 80th in the country last year in total offense. Given the choice, I would choose players from higher octane offenses.
The move to a new conference hurts WVU from an opponent familiarity standpoint. But that goes both ways. We've started doing out EOS (ease of schedule) calculations and we see WVU making the biggest leap in this category (in a positive way). Big 12 defenses have not faired well of late. Of course you could argue that is a by product of a lot of strong offenses in the conference...but WVU has a strong offense. On paper WVU's schedule looks significantly easier. Texas and Oklahoma would be the only two games that worry me.
Plus you nailed it right on the head. Year two of the Dana Holgorsen and the entire passing attack returns. They should be even better in 2012. I see more reason for Gino Smith to improve on his 2012 numbers, and less negatives than with the other 3. I would keep Smith.
FWIW, here is where each was drafted in a mock we are currently doing with Athlon:
Randle Pick 4
Smith Pick 11
Oliver Pick 14
Harwell Pick 26