My dad is an electrician so he did it for me, from what he told me it was pretty straightforward. The easiest thing to mess up is the orientation of the toroids, which is easy to notice because the values will be negative. The 120A toroids are also kinda bulky, if your panel is on the small side it might be a bit difficult getting them in there.
Yeah the bigger toroids are quite expensive, you can always buy just the toroids by themselves later on though, I think Shelly even sells them separately
I have the Shelly Pro 3EM 120A and I have nothing but good things to say about it, installation is easy if you know what you're doing, integration with HA was trivial and it's very customizable. Before purchasing it I was worried about the update frequency of the values, but I was happy to see that it updates about a couple times per second, which is great. I'm happy to answer any questions you might have!
What's even cooler is that the nRF52840 chip that they will use has ZigBee support, which theoretically means it can talk to your network directly if software supports it
You can use the same compose file with podman for the most part