I see that Bulkheads are bought as a System, and add 10% to the vehicles Base Hull Value. Question: Does this 10% get added before or after the costs of other systems that are reliant on BHV for their cost?

In short (hypothetical only):

I have a vehicle that has 40 BHV based on the construction chart. I add Bulkheads, so I now have 44 BHV.

I also buy a system that costs me 50% of my BHV in points. Does it cost me 20 points, or 22 points?

Thanks,
Kealios

It's added to the BHV, prior to adding any components. In your example, 22 points would be correct.

There is no entry for Bulkheads in the SW Construction list for Systems, so I am assuming that the increase of the BHV is cost enough, eh? In other words, if I choose Bulkheads, I dont need to buy a system called "Bulkheads" - as long as I increase the BHV and then base all future cost calculations off that new BHV, Im good, right?

Correct; it's a modification to the base hull, not a system.