It would be a good time to start experimenting with the grand unified
index of Scheme libraries/packages. It'll be a long project, so best get
going early.

First off, should that be library or package?

lib.scheme.org
libs.scheme.org

pkg.scheme.org
pkgs.scheme.org

Most languages have a _package_ manager, where a package is a collection
of libraries (+ some auxiliary files). I don't know about others, but
I've always found this two-layer approach confusing.

R6RS and R7RS only talk about libraries, which are a logical and easily
understood unit that ties neatly into the language semantics. By
contrast, a collection of libraries is an administrative concern. If I
want to import library (foo bar baz), do I really need to know which
collection it comes from? If the library comes from a particular git
repo or tar file, can't the package manager find that collection for me
and figure out how to extract the library that I want (as well as any
other libraries that it depends on).

Package managers need to do dependency-chasing anyway in order to
resolve packages that depend on other packages. It shouldn't be more
work to do that on a library level as opposed to a package level.