Also: Is it possible to only sync part of a Jira project data to Ketryx?

Yes, it is possible to have Ketryx only track parts of a project. This can be implemented in a few different ways: 

Issue types

Entire issue types could be untracked by Ketryx. From your Jira instance, you may want to perform the following to include / exclude issue types from your project. 

1. Click on Project settings
2.  Click on Types under Issues
3. Click on Actions followed by Edit issue types
4. Choose which issue types you'd like to be available for your project and save

Individual configuration items

Consider using a KQL filter for "unchecked" items, i.e. items that do not need to be controlled before a version can be released. By default, no items are considered unchecked.

Configuration item fields

Portions of issues (e.g., specific fields) can also be untracked or uncontrolled, and we have additional flexibility on what information appears in documentation via a robust document template feature.