Add-on Auto thread for every 1000 posts or milestones

Hey there,

What I am looking for is a widget/block that shows let's say the last 5 users who got recently their post counter to a round thousand (like 1000/2000/3000/.../etc.). We had this in vB but I'm not quite able to find something similar for XF.
This is my basic wish.
The next step would be to create a greeting thread for the user who reached the next full thousand in his/her counter.

As an alternative I created milestones for every thousand posts. I'm looking for a possibility to create new threads automatically for reached milestones.
That is the big shot.

As a benefit it would be possible to auto create a thread not only for the 1000 posts but for ANY custom milestone created.

So is there an Add-on in this direction?

If not, I would like to try to create a new one in my spare time. My problem: I've not much experience in XF-coding. Lets say I want just create a XenPorta or advanced widget Block that displays the last 5 Users with full thousand postings. what would be the recommended XF-way to accomplish that?