If you don't do any gaming, photo/video editing or 3D modelling, you don't need a dedicated GPU, but make sure that either the motherboard comes with on board graphics or that you get an APU (processor and graphics card combined).
Regarding PSU, I don't know where he's getting 450 W from, but you can use a PSU calculator to see what's the minimum power your PC needs.
https://outervision.com/power-supply-calculator
https://www.bequiet.com/en/psucalculator
Both calculators above are well regarded, the Outervision one is more complex. Just input all the parts you intend to get (also parts that you think you might upgrade with in the near future) and hit calculate.
Bronze/Silver/Gold/Platinum standard refers to how efficient the PSU is. I think Bronze is around 80%, so a 450 W Bronze standard PSU will actually only provide 360 W. The spec sheet will tell you how efficient the PSU is and I would probably aim for 10-15% over what the calculator tells you that you need (just in case).