2. How much storage is available for tracks?
The unit stores 10,000 trackpoints internally. By default, only 3,000 are shown but that can be changed in the Map setup/Tracks tab.
Essentially unlimited storage can be used by storing tracks on the memory card in setup.
3. What is the active track vs. saved tracks?
The Garmin GPSMap 60CSx keeps three kinds of tracks: active, saved, and stored.
Active tracks have elevation and timestamps. They are the most 10,000 most recently recorded position points. Active tracks will either overwrite the oldest points if set to wrap or will stop recording and display a message if you set it to fill.
Saved tracks are created manually by the user from the keypad. Saved tracks are 'compressed' by the unit to have under 500 trackpoints and have neither elevation nor timestamps and have fewer stored trackpoints.
Optionally, the unit may write tracks to the removable SD memory card as GPX files. These files are immune from the limit of 10,000 points, the settings mentioned above and the compression of saved tracks so they always have timestamps and alttudes. These files can be read by your computer, but the GPS itself will never display them.