deposit depends on total price, perhaps take around 5% of the asking price when you inspect, so 100 for a 2000 car.
i like to inspect at the other persons house unless it's drastically inconvenient - people are gonna be less likely to rip you off if you know where they live.
all in all you don't hear too many horror stories about the purchase process, more about a car dieing after, so make sure you know what you're lookin at and do a thorough inspection