Periodically check the oil lines (assuming you still have the oil injection system). Oil line coming off is common failure point. Consider going to pre-mix......something I would consider doing on any older 2 stroke ski.
Might want to check if the previous owner fixed the power valves with clips. They have a tendency to fall into the cylinders..........not good. If not fixed, consider fixing them yourself.
Other common failure point on those skis is the catalytic converter, especially on one that is 10 years old. If the cat/con hasn't been replaced with a "D" plate you might want to consider doing it yourself.
Other than that, keeping the carbs. clean and rebuilding them when needed is probably the biggest maintenance headache.
The 800s are fun skis to ride, but can be a PITA to keep running.