Hi @Lisa Bolds
1) You can set up a private channel and only include project team members + guests in this private channel.
2) Unfortunately, to grant a guest access to a team they will need to inherit the access to the General channel. (As you will add them to the team, and then manually add permissions to the private channel). If you have other private channels, the guests will not be able to see those.
Private channels in Microsoft Teams
https://learn.microsoft.com/en-us/microsoftteams/private-channels
If this is helpful please accept answer.