If I switch out of a career before finishing it, and then for some reason were to switch back to that career would I pickup where i left off in terms of career advances and the like or would I start anew?

Yes, you would start with the advances you had already spent marked off.

Page 47 of the Player's Guide

When moving back into a previous career, the player should refer
back to the character sheet he had during his previous career, making
note of which advances had already been completed. In this
regard, a character returning to a previous career he had not yet
completed picks up right where he left off. Jumping back and forth
into the same career does not refresh the advancement options.

Missed that bit, thanks!