I'm still rather skeptical of it being Russia, or any of the above having a clue who it was. The DNC/Podesta security was a complete laughing stock, and AFAIK, the only people that have actually looked at any direct evidence are Crowdstrike, who will blame any nation-state for any attack if the money's right.
As for why Russia would have an interest if they were truly to blame, it's not rocket science. Clinton supported a "let's escalate to WWIII with Russia" policy (no-fly zone in Syria), which Russia has obvious and rational reasons to be against. The downside for the Ruskies is that hawks like McCain are trying to goad him into the same stupid policies.