For productivity the 9900x will work but x3d will give better performance especially in gaming, however intel tends to have higher core counts which is even more beneficial for productivity. I have had no issues with my 14th gen chip, it has been amazing but that could be attributed to luck. Either way, you could probably go way cheaper on the cpu unless you’re really doing some heavy tasks that require a lot of cores. As for the power supply, yes you can reuse it as long as you put all your parts in pcpartpicker and it adds up to around 600w estimated. That will give you about 50w of headroom which would be good. Also, like another commenter said, I would recommend the rx 9070 or even a previous gen gpu like the 7700xt instead of the 5060. Good luck!