I am no expert by any means, just parroting what I have heard.
Do you use HPA? It's more consistent than C02.
I believe a regulator will help consistency, though HPA tanks have one built in. I do not know if a reg on a gun on top of an HPA reg will be a benefit.
And as far as I know, the most important thing is quality paint. Since you're using pump you could probably afford to buy nicer paint, which will probably help you the most.
I do use HPA. And as far as nicer paint goes, I would totally buy better paint, however the fields I go too do not allow use of any paint other than theirs.