I'd have no worries running a 5600G on a 4 pin connector. Now, as to the PSU...I'd have to say 450W, especially a Bronze unit, is quite substandard in modern systems. If not running a discrete GPU it will probably be OK but if ever upgrading to one be sure to factor in the cost of a new PSU along with it. I'll leave others to critique brand and model...if it's needed.
You are good.
Are you using the 5600g graphics, or a discrete card?
Aux cpu eps power is needed for High powered processors, overclocking or multiple pcie graphics cards; none of which you have.
Some motherboards will require that the connector be plugged, regardless if the power is needed or not.