aight,here is what i would do.
Keep the SSD,HDD,GPU,everything else sell.
PCPartPicker Part List
CPU: Intel Core i5-10400F 2.9 GHz 6-Core Processor ($166.99 @ Amazon)
Motherboard: MSI Z490-A PRO ATX LGA1200 Motherboard ($159.99 @ Best Buy)
Memory: Corsair Vengeance LPX 16 GB (2 x 8 GB) DDR4-3200 CL16 Memory ($78.98 @ Amazon)
Case: Phanteks Eclipse P300A Mesh ATX Mid Tower Case ($49.99 @ Newegg)
Power Supply: Corsair TXM Gold 550 W 80+ Gold Certified Semi-modular ATX Power Supply ($79.99 @ Newegg)
Total: $535.94
Prices include shipping, taxes, and discounts when available
Generated by PCPartPicker 2021-01-22 16:41 EST-0500
This should be able to last you without upgrading anything for 5 years.
The motherboard i put in supports the new Rocket Lake 11th gen intel cpu's lineup,which you can upgrade to any time you want,but i dont think 10400F will be in need of upgrading any time soon.
I said keep the GTX 760,until this graphics card situation cools down.
If you were to buy a GPU now,you would spend all your money on a 1660 super,which would not be wise.
Your powersupply is pretty old and pretty bad,so you should replace it.The unit i put in this list is efficient enough to power a 3070,so you should be good on that.
The main reason i want to upgrade the CPU/MOBO/RAM is because Haswell (4th gen intel cpu's)is a dead platform and it would honestly be a waste of money upgrading to i7 4770/4790,when you have 500 euros to spend.
After this GPU situation calms down,you should be able to see 1660 super for 300$ new,on the used market they ussually go for 200-250$