Hmm... I'm not sure I get it. :)

• Is this about creating milestones directly under https://phabricator.wikimedia.org/project/subprojects/349/ ?
• Or about creating a new subproject under https://phabricator.wikimedia.org/project/subprojects/349/ and then creating milestones in that new subproject?
• Scope: Deployments states it is about on "Tools to deploy code on Wikimedia servers / cluster" while you're mentioning tarballs in the task description?
• How is MediaWiki-Release-Tools related? :)
• Also note that milestones have a certain order. See for example the "Previous" and "Next" links in the sidebar on https://phabricator.wikimedia.org/project/view/3920/ . (Maybe you want subprojects instead of milestones? But still not sure where.)

Let's number these:

1. I was told "milestones" and didn't realize there was an actual thing in phab called "milestones" before reading the docs you pointed me to. I initially thought the documentation said you milestones had to be under projects, not subprojects, but now I see that they can be under subprojects. So, yeah, putting it directly under Deployments isn't needed.
2. Upon reflection, and taking into account your other questions, this could be a new subproject with these milestones.
3. If there is a better project (like Release), I'm all for it. I'm not tied to anything right now.
4. I asked for a project to use and was given MediaWiki-Release-Tools. I would say I'm creating a tool and it is for MediaWiki releases.
5. These have an order, but your example is date based. If milestones need to be date based (that seems easier to organize at the outset), then I'm all for that.