Hello,
I would like to become a packager sponsor and help with the long queue
of packages waiting for a review and sponsorship.

Maintain at least three packages

At this moment, I (co-)maintain 28 packages
https://src.fedoraproject.org/user/frostyx/projects
7 of them are my own packages, the rest of them is co-maintained.

Have done five high quality, nontrivial package reviews

It's up to your assessment of what is "high quality" and "nontrivial" but
I've done ~16 package reviews.

https://bugzilla.redhat.com/buglist.cgi?component=Package+Review&email1=jkadlcik&emailassigned_to1=1&emailtype1=substring&list_id=12890880&product=Fedora&query_format=advanced

Have been members of the packager group for at least one release cycle so that they have seen the process of branching for a new release.

I was sponsored into the packager group in 2015 and maintain
packages since then.

Apart from packaging, I am interested in the package review process
itself. I have created the Fedora Packager Sponsors page
https://docs.pagure.org/fedora-sponsors/

And implemented opt-in support for running the fedora-review tool
after every build in a Copr project
http://frostyx.cz/posts/running-fedora-review-after-copr-build

Though I don't want to take all the credit for it, both were original
ideas from @msuchy.