Fitbit don't appear to have released the exact specs but one review stated there was 2.5 GB of storage - what they don't state is whether thats locked to just music or its the total storage which is shared between apps, music, OS etc (plus 1 watchface at a time - which is an annoying limitation). However, unless you are installing dozens of apps (and the interface just isn't designed for scrolling through so many anyway), I don't think it will be a problem as they are pretty small. You can also remove most of the built in apps via the phone app to free up some storage / screen space if its a concern - click on the watch in the app, then apps then all apps and finally the app you wish to remove and scroll down the page to 'remove' - works on starbucks, strava, even the music app - basically everything except the core ones like exercise, today, alarms, settings and weather.
