I don't have any experience with a Pi to really give you any insight on that end. I would think modern cpu should be able to handle it. The challenge might be with single NIC.
Just to give you an idea, I have an old NUC and on average it consumes 20% cpu and about 14% memory(8GB), at the most the network sees 10 devices.
The little guy is an Epyc 3101 and it replaced a VM from an old Xeons 2xxx series. I gave the VM two cores and 8 GB. Average was 15% CPU and about the same usage for memory. However that network has more power user and devices. With the Epyc, I barely sees any CPU usage and I combined it with 32GB of memory at about 2% average usage. About half a Gig usage on memory compare to 1.5 Gig with the VM. This is not a scientific statement but my own personal observation. Don't quote me on this but I recalled seeing requirement for PFSense for high usage was at least 3ghz CPU. The 3101 turbo at 2.9 only. I upgraded my ISP to 1G and tested download and stream at 2K and 4K with no issues. Mind you, I didn't have many VPN sessions going though. I am planning on upgrading my network to support 10GB that's the reason for the Epyc, just to learn more than anything else. Anyhow, I will try to get my hands on a Rasberry Pi, for the price I should get one and play with it. Looks like there are few options to add extra NIC for the Pi.