Tools for the work as proxied maintainer
From Gentoo Wiki
Document your Gentoo knowledge
app-emacs/org-mode or x11-misc/zim will help you to accumulate your knowledge fast and find everything quickly later.
Compare and merge ebuilds (diff)
GUIs like dev-util/meld and command line tools like app-misc/colordiff or dev-util/imediff2 help to compare ebuilds.
app-misc/colordiff simply prints a colored diff
3-way merge in dev-util/meld
2-way merge in dev-util/imediff2
kde-apps/kompare visualizes what a patch will change in the upstream source
Every proxied maintainer has to test packages before committing them. A test environment can be useful.