CNSA did acknowledge that they benefited from prior explorations to mars done by everyone, including NASA, soviet union, ESA and more. They are able to find general scientific data on mars, such as atmospheric density, composition, potential weather events, general topography in the public domain (I mean, wikiepdia has a lot of these information). For these, they should and are appreciating scientists going before them are sharing these information in the public domain. But I am sure NASA and everyone else did not release all super detailed data, such as detailed topology maps. And from public available info, they also know about general designs of NASA's landers and rovers, and the troubles NASA has faced operating these crafts on mars. If they learn from NASA's experiences, they can avoid a huge amount of unknowns and negative encounters. These are significant assistance when you are engineering systems. The pioneer is always way more difficult. So of course respect is paid and hats off to NASA and other pioneers.

But knowing these are not enough for you to build and operate a fully successful mission. Even if you had the entire CAD file of a NASA lander and rover, you don't know why they are designed that way, you will not operate, use and troubleshoot issues correctly. You need to build the system from ground up, so the people on your teams have full understanding of every single "why" and "how". Only then will you have full control and ensure the mission is success.

I am sure you had experience taking ownership to a software project written by others. You always have go to the original designer to ask "why" and "how". The knowledge transfer often last months and countless meetings. If you don't fully understand, you can't fix issues or build new features. Most people would rather build their own then to fix something they don't fully understand.

For CNSA, they can access public available data. Then they have to simulate, wind tunnel tests, how to land, what shape of lander they need, how to balance and control the lander etc. They need to build up their understanding of the entire system. They actually has been improving their technology and understanding of atmospheric and controlled powered landing from earth and moon missions. One of things they did differently is adding a flap to the lander to stabilize it in flight, they said it was to increase the lander's robustness when encountering more extreme weather.

For solar panels, knowing the distance to the sun, the atmospheric density, pressure, composition, force of gravity on mars, you can estimate the theoretical max of the solar energy available per unit of area. Then you could say assume only 30% is available due to weather. I am sure they have more advanced ways to estimate. Interesting fact about the rover, it has a solar heat capture and retention system. And they use the heat for thermo-control at night instead of electricity captured from solar panels, saving electricity use.

For where to land, topology and maps of mars is in public domain. You can find a general region where to land but these data are not detailed enough to actually land. And mars surface could have changed since these were captured. So tianwen-1 contains a orbiter and the lander. The orbiter has instruments such has high resolution imaging. They arrived mars orbit in February, and the 3 months since the orbiter was collecting data on mars. From these data they finalized their landing plans.

This is China's first spacecraft to ever travel this far. They also don't have communication network between mars and earth. So Tianwen-1's orbiter is also a communication satellite.

The impressive thing is the engineering side, how they engineered the system that each component all worked correctly in one go. The rocket: the rocket required to launch tianwen-1 (weighs 5 tons) to mars orbit was only tested successfully in dec 2019. China also doesn't have earth mars communication satellites and fully operational deep space communication system before this mission. This the first time all these system are tested live. To fly a spacecraft to mars for the first time, have it being captured by mars, and orbit mars correctly. Take data on mars. Release the lander. The lander going through atmosphere, releasing parachute at super sonic speeds, the lander detaches from parachute and uses a rocket engine to fly. At height of 100m, optical imaging and laser maps out the ground and autonomously navigate the craft to soft land on flat ground. Orbiter forms communication link between mars rover and earth. Mars rover collects sun light, drives, survives the elements of mars (so far).

Overall, they are standing on the shoulders of people who went before them. One shouldn't look down on their success, nor should they over-hype their success.

CNSA said Zhurong landed 3km away from their designed coordinate. For the first 42 mars days, zhurong traveled 236m.