Could the order numbers be global across all of their product line?
Global, likely; across all product lines, unlikely. I believe they are separate lists - Gavin could comment, as he is on both the E+ and the Empulse list.
How many Enertia bikes have they sold?
Unknown - one person on elmoto
claimed 50 Enertias sold, but did not back his claim with a source. I suspect the number is in the 100-300 range.
I recently made a reservation and got an order number 1716 - are their really 1700 people waiting for the Empulse? Could they have sold less than 1700 Enertias to date? I have no idea what ballpark either of those numbers are in...
Very likely there are 1700 people on the preorder list for the Empulse, though nearly all of them have placed a preorder with an expectation of a $10-14k bike. I would expect only a few hundred of those to turn into sales at $18-20k .. which may still be several months of production. Once the Empulse starts getting press, magazine reviews and whatnot, more interested buyers will turn up that weren't previously aware of the Empulse.