Redmine

I'm considering going all in on Redmine but want to understand some things before I pull the trigger. So far I've been able to test that commits and activity in sub projects show up in the activity for the parent project. How do ticket references work between projects? Especially when it comes to commit log referencing?

I want to get some idea how to best organize things. How a project and its sub projects interact with each other will probably have a big impact on this. One layout I've been considering (but only works if they can all communicate with and reference each other):

Parent project (has all the issues, milestones, discussions, etc.)
- Core sub project (mainly repo for core)
- Packager sub project (mainly repo for packager)
- Sub1 sub project (extension to project that isn't a part of core)
- Sub2 ... etc.

I'm not sure how well it will work to actually have discussions and issues down in each project. It might start to get lost. However, it seems more logical that way. (tickets specific to packager can live in packager sub project) Will all of the issues aggregate under the issues tab on the main project? If someone chooses to create a "New issue" from the main project, can they actually create tickets for sub projects?

I realize this post is kind of all over the place. For that I apologize. Hard to figure out how to ask this question in several smaller ones... and I don't really have the time to set up three or four projects to see how they all work together otherwise and try to figure out how to configure them.