We always envisioned that the printer would be upgradeable to up to 5 nozzles from any of the lower configurations. However, that was before we added the water cooling. The cooling unit will be the same no matter how many nozzles you have, but each nozzle requires a cooling block that will now be considered an extra part, and will require you to install it if you buy it after the fact. If you are a handy person then you won't have a problem.
We have not set pricing on a standalone extruder, hot end, and cooling block. We are committed to the Kickstarter pricing, but the design has changed over the course of our campaign, and the price of an entire printer is going up once the Kickstarter ends. So as long as you are prepared to pay more, later, for the extra pieces than you would have paid had you bought them all now, then go ahead and pledge for a printer with fewer nozzles.