Does it possible to play multiple cards from hand during the capital phase, as long there are still unused resources.

it can be understood from the rules that each player restricted to play one card only, because according section in the rules uses everywhere a singular form of "card" and not "cards" (see p10 section 3).

yes, you can play as many cards as you have resources to pay for. Of course, only 1 "limited" card per turn, 1 hero per zone, 1 copy of any given unique card per player in play at any time, etc.

thanks for the clearifications

I missed the two rules about heroes and limited cards

what do you mean by etc, there are some more limitations ?

not that i can think of at the moment, but that doesn't mean that there may be another in the future

The reason everything is singular is because only one card can be played at a time. The part which discusses you can continue playing multiple cards is where it talks about each player taking actions one after another (and that playing cards is considered taking an action) until both players pass consecutively.