How can I make sure the iTC is an open forum that everyone feels welcome to participate in?

This is a difficult question, but there are some things that can certainly help. The first is to establish a code of conduct. While some of this is laid out in the ToR templates we have been using to create iTCs, it is helpful to be more explicit about how to contribute to the iTC and the expected conduct for doing so (as well as establishing possible penalties for violating the expectations).

A place to start is the Code of Conduct here https://github.com/itc-wgtools/iTC-docs/blob/master/code_of_conduct.adoc. This is included in the iTC administration template and is based on the Contributor Covenant for open source projects. Setting this as the expectations for the iTC will set the rules for conduct.