When you uncheck the Enable checkbox on the Suricata INTERFACES tab, that Suricata instance will never auto-start (even on a pfSense reboot). But if the Enable box is checked, the interface will auto-start upon a reboot of pfSense even if the interface had been manually stopped before the reboot.
One perverse thing with Suricata and the way it handles TCP sessions and flows is that the more CPU cores you throw at it, the more RAM it demands for the TCP Flow/Memcap parameter. Start simple with just 4 cores assigned to Suricata and 4 GB of RAM in the virtual machine.
And start with Legacy Blocking Mode instead of Inline IPS Mode. Legacy Blocking does not bring in the netmap kernel device and thus will likely bypass any issues existing there in Proxmox. And as I said earlier, you really can't successfully use VLANs with Inline IPS Mode (at least not without a lot of weirdness up to and including random crashes).