Your CPU will likely have no issues if you update to the required BIOS. This would require you to have a CPU that already works in the system in some cases. Looking at the rear IO of that board it seems that there is no "BIOS flash" button.
Using a PCIe 4.0 GPU in a PCIe 3.0 slot, in some cases, you will get about the performance within margin of error. In other games you can see anywhere between a 10% to 20% decrease in FPS using PCIe 3.0 versus PCIe 4.0. All of the games I looked at were very playable on both PCIe 3.0 and PCIe 4.0 with the RTX 4060.
In your case I suggest looking at the B550 offerings online, at some point, as they are relatively inexpensive. While looking around, remember to look at reviews regarding VRM temperatures because some boards VRM cooling is more robust than others.
Furthermore, while looking around the internet, I found that If you want to get the most out of the Ryzen 5000 series most users suggest looking into memory with XMP of 3200mhz to 3600mhz.
In conclusion using your current setup should be fine if you are targeting playable framerates, as opposed to super high FPS gaming.
I am having a hard time finding tests of the DLSS 3.0 Frame Generation performance differences between PCIe 3.0 and 4.0.
I hope this helps.
Ryzen 7 7700X, MSI MAG X670E Tomahawk Wifi, Corsair DOMINATOR® TITANIUM RGB 2x16GB DDR5 DRAM 6000MT/s CL30, Sapphire Pulse AMD Radeon RX 7900 XTX, Corsair HX Series™ HX1000, Corsair MP600 PRO NH 4TB
