What would you suggest?

What colour do you actually want?

Lighter brown/dark blonde

Could I do a level 6 blonde? A 6 ash brown is darker than I want to go

level 6 blonde and level 6 brown are the same level, call it blonde if you like it is still the same.
If you want it cooler, more ash toned than it is now you need to go one level darker. So if it is a level 8 now, you need a level 7 if you want to cover the brassiness

Thanks for your guys help, I know I'm probably driving you guys crazy but I just want to be careful.

Last question, is it safe to do a demi right away?

The lower the peroxide the less damaging. Ideally waiting before processing again would be better, or not processing again at all and using direct dyes to get your goal colour.

I thought a demi was a direct dye?

No a direct dye uses no peroxide, and is completely safe to use whenever.
A demi permanent usually has no ammonia and uses a lower vol peroxide than a permanent dye, but works the same way.
If you can get direct dyes in natural shades (Adore make them) or can mix your own from unnatural shades eg Manic Panic, then that is what I would do as it is the least damaging route.
I think for you a low vol demi might be easier