Is there a general rule of thumb for the excess amount of resin to apply to CF part above what is needed for saturation? e.g. if i calculate i need 500g of resin to saturate my part,  how much should i apply to my part during the hand layup?

It also makes a difference how you use your resin. The first layer should be applied very resin rich, and every following layer with less resin. If you use vacuum compression, the last layer could be applied almost without resin.
But if you use vacuum compression, I would not bother with wet layup anyways and switch to infusion, with gives better results for the same amount of work.