But one thing bus me, essentia points. How exactly do they work? Do you expend them for any length of time or merely assign and reallocate them as you wish?
The latter.
As a swift action "Divert power from the engines to the shields!", that kind of thing. Two exceptions that come to mind:
Incarnum feats have essentia invested into them at the start of the day, and cannot be adjusted for 24 hours.
The soulcaster can invest essentia into spells, which cannot be removed until the spell is cast (after which it returns to your normal pool).
There is a limit on how much essentia you can put in a single receptacle based on character level (normally maxing at 4), though certain abilities let you overcome this. This is why the ability to bind a soulmeld to multiple chakras is good - you're fueling two powers with one pool.