Not trying to make the choice harder, but mailbox.org seems to fit into the choices as well (also hostesd in Germany). Also in terms of hosting in Switzerland, keep in mind that it’s not actually part of the EU, which is the primary/original source for many of the privacy laws you probably care about if you’re looking into these providers.
Basically OpenWRT is for dedicated, purpose built hardware, highly compact and essentially “embedded”. OPNSense is for running a (potentially much more capable) firewall on x86/x64 (even if it’s a small specimen like N100 or whatever). They fill a somewhat different role.