I’ll have a look at prices for a new cpu and gpu while keeping the psu.
In terms of swapping the pcs drive out for the WD drive would I have to repurchase windows for the WD drive as the pcs drive is my boot drive?
Just be careful with the GPU. As much as you can check the TDP there is a big difference nowadays with what that actually means. Transient spikes are a big issue in more modern gpus where they can draw double the TDP rating and cause instability/BSOD if the PSU isn't up to the task (the 450 simply isn't).
If you login to microsoft with your current system you will be able to link the key to your account (If you haven't already). When you switch out the drives simply login again and it will activate. No need to purchase another license.