THe card states that "Action: Spend 2 resources to have a target unit gain 1 power until the end of the turn"

Can I keep pumping the same unit up by paying the 2 resources cost until I run out of resources? Or would I need 1+ Runesmiths to do this?

I can target any unit in any zone even my opponent correct?

So if I had 8 resources I could pump a unit up to 4 power plus his base power?

thanks

It is my understanding that, yes, you can do that because there is no limit to how many actions you may take at any given time.