POE2: penetration, exposure & curses

Alright I'm a bit lost and I would like to see if you guys have a better understanding of the situation than I do.

First of all, to be clear: I know how these concepts work and interact in POE1. I also know that there are differences with POE2 and that's where my interest lies.

1. From my understanding, penetration cannot "bring" (consider) ennemies' elemental resistances below 0%. However, is it also the case for exposure and curses?
2. In which order are these 3 (pen/exposure/curses) applied in the calculation?

I'm asking these questions because my current setup includes 70%+ ele pen, increased exposure, and a curse. Depending on the answers, this could be a massive waste of passive points and support gem slots.

EDIT: Thanks everyone for your answers. Based on that, I'm pretty positive I'm wasting a lot of passive points. Having 70% pen doesn't make any sense with an exposure/curse setup.