Yes you can have multiple characters.

Now as for power stuff well I don't think we will do blast cores/shards because those were caused by the ray sphere (blast shards) and the explosion in the beginning of Infamous 2. The relays are a possibility but then again with no need of the DUP would those still be around is the question, would the CTU have them? I'm undecided.
Now power fusions, if you mean what Cole did in Infamous 2 that gives him ice or fire I'm going to have to say no too. Only really powerful conduits seem to be able to even get anything out of it like Cole was since neither Kuo or Nix gain anything out of it despite it being a two way street.