groundFungus:
You should not be powering the A4988s (apply to Vdd) from an output pin. You can control (step, dir, enable pins) many from 1 output pin. 3 should be no problem.
What's the purpose of the 5V pin then, if not for powering devices/components that need low power? I'm doing it this way because i'm trying to reduce my installation to the minimal amounts of parts.