Jira missing 3 items to easily import/export issues via csv from one project instance to another

I am implementing Jira at a large company and we are looking to migrate a project that is currently hosted at a vendor site. After a few hours iterative importing/exporting via csv I have 90% of what I need, but the remaining 10% is important and not available:

1. Comments (showstopper): I can't export/import all/any comments via csv, and this is a dealbreaker as all issues have a variety of comments. Workaround = https://marketplace.atlassian.com/plugins/it.skyit.jira.plugins.all-comments-cf
2. Watchers (High): Similar to comments I would like to be able to export/import all the watchers of a given issue via csv

This just leaves attachments, which obviously can't be exported via CSV but hopefully I can get the Vendor to have them all copied over here.