I am only going to address the third question since @RedGrittyBrick already answered the first two.
How much accurate they are?
The accuracy of the speed and location of spacecraft depends upon the distance from Earth and the amount of money spent on the attitude systems.
The distance matters because when close to Earth, they can use interferometry between multiple ground stations. Then the accuracy is limited by the accuracy of the spacecraft and ground station clocks. On GPS spacecraft, the clocks are incredibly accurate and we can determine their location very accurately. On other spacecraft like Wind, located at the $L_{1}$ point, the location does not need to be known to better than few tens to few hundred kilometers. This may sound like a large uncertainty, but the spacecraft is located ~230-250 $R_{E}$ (or ~1.5 million km) away from Earth (or something like ~0.007% uncertainty).
The speed of the spacecraft can be determined using a combination of the interferometry, Doppler effects from the transmitter signal and/or radar, and orbital element predictions (see more in this article on orbital mechanics and this article on flight dynamics). Again, the accuracy depends upon the distance from Earth and the amount of money spent on the attitude systems.
Some missions buy specific atttitude systems to ensure high accuracy in their attitude/orbit determinations while other missions rely upon some of the methods I mentioned above using the Deep Space Network or the Near Earth Network, depending on altitude.
