We learned that the ContributionTracking extension is deployed to donatewiki so if we could do another deploy once the new design is done, using that is one options.
We just discussed this. Since the payments maintenance page is not mobile friendly (https://phabricator.wikimedia.org/T253318) and a bit more difficult to edit, we agreed to use Template:Lp-layout-maintenance which keeps the user on donatewiki. I can make it fall back to the MediaWiki:Contrib-tracking-fundraiser-maintenance-notice translations for languages other than English, will work on this tomorrow.
I'm also happy to switch in the maintenance message on Monday.
For the footer there isn't a black WMF logo button yet, and there appears to be some contention about it (see T174603). I would recommend just sticking with the current one for the short term.