Range is line of sight. If you can see it, even if 100 miles away, odds are it'll work. Seattle area has one of the better networks for MeshCore. Tacoma to Vancouver BC is the range for semi reliable messaging
Yes you can get decent reception inside buildings. It operates in the 915mhz band. Similar frequencies to old school pagers. Lora is an interesting RF protocol, it has really good properties for operating below the noise floor.