Major addition to existing non-LEED building

I am working on a 4,000 SF addition to an existing 8,500 SF fire station constructed in 2003. The project will add another vehicle bay and some dorm rooms/support spaces. Originally, the addition was going to be registered under LEED-NC, but the central HVAC system for the addition was value-engineered out of the design (among other things) so I am now looking at LEED-EB for the combined structure. The addition will now have through-wall HVAC units in the dorms rooms. The design right now is to expand the vehicle bay and add the dorm rooms much like another wing; the only way to get from the new dorm rooms to the existing rooms will be through the (expanded) vehicle bay. How can I approach credits for issues like energy/water performance, when nearly half the building I intend to register has not been constructed? I can document the various "plan" credits easily enough, and there are more like WEc1 where I can just make sure the entire facility will meter water. Any suggestions on how to approach EB for a building that has partially yet to be designed? Should I be looking at NC for such a small project?