1) I think the save DC's for the class abilities should scale with class level. Since these abilities are at will, maybe make it 1/2 class level, but I'm not a fan of fixed DC's, it just means that your class abilities become useless at a certain point.

2) Do the hammers from Hammercall qualify for Hammer Bond?

3) You need to specifically state whether or not the increase in critical range from Hammer Bond stacks with Improved Critical. I'm guessing it doesn't, but this is one instance where absolutely clarity never hurts.