If I have this correctly (and Im noob at this). The Power Dice are the black dice and the Combat Dice are the Red(melee) Blue(Ranged) and White(Magic).

If this is true does this mean that when it says "you may only roll 5 Power Dice at once" that it only it only refer to the Power Dice and so you could roll 5 Power Dice on top of rolling other dice from items/weapons ect?

The limit of 5 power dice per attack applies only to power (black) dice. Any other dice you may be entitled to roll do not count against that limit. Also, that limit applies only to attacks, so you can roll more than 5 for things like the Cloak of Deception (copper treasure).

Thank you for your time in making a perfect answer.

Also keep in mind that you are only ever allowed to attack with ONE weapon per attack. So dual-wielding crossbows would be a bit of a waste. Better to grab a shield...