The following is a post I recently made on the SustainOSS Discourse forum. It was in response to this thread and, more specifically, this post. Unfortunately, my post was deemed spammy by Discourse's algorithm.
So, for Anatoli's benefit, I'm republishing my response here:
Fair questions, Anatoli. I'm happy to provide some rough metrics (I don't have precise time info). I maintain a lot of services on behalf of my employer (the [OER Foundation](https://oerfoundation.org), the charitable foundation for whom I work as "Open Source Technologist") and the [NZ Open Source Society](https://nzoss.nz) of which I'm the deputy chair (was the Chair for 9 years before stepping back a few months back), a voluntary role. Here's a list of systems I run (all Docker-based, where ever possible):
* a bunch of Drupal 7 & 8 sites (like https://nzoss.nz, https://tech.oeru.org, https://openstandards.org, and this site, https://davelane.nz)
* a few WordPress multisites (like https://course.oeru.org) and a bunch of standalone WordPress instances (https://coep.nz, https://oer4covid.oeru.org)
* 4 Discourse instances (https://community.oeru.org, https://forums.oeru.org, https://community.nzoss.nz)
* 4 NextCloud instances (with CollaboraOffice and OnlyOffice servers for each)
* 2 BigBlueButton instances (along with TURN/STUN servers)
* 3 Mautic instances
* 6 Rocket.Chat instances (like https://chat.nzoss.nz)
* 2 Mastodon instances (https://mastodon.nzoss.nz and https://mastodon.oeru.org)
* 3 Mailcow instances (a full multi-tenanted SMTP/IMAP/POP email system with active spam filtering, user self-service, DKIM configuration/management, webmail, & much more - even virus scanning for Windows clients ;) )
* a YourLS link shortener
* a Matomo instance
* a Mahara instance
* a Moodle instance (https://moodle.oeru.org)
* a SilverStripe instance (https://oeru.org)
* a couple MediaWiki instances like https://wikieducator.org
* a couple GitLab instances (https://git.oeru.org, https://git.nzoss.org.nz)
* a couple LimeSurveys (survey tool)
* a few BitWardens (password managers)
* a couple Etherpads
and many more...
The idea is that when I work out how to set up any one of these FOSS services, it's easy to set up another one of the same for someone else, and the maintenance requirement for 2 is perhaps 10% more than for one... I'm amazed at how much time I have for actual development work (I've also had time to work on a lot of this: https://git.oeru.org/explore as well as a similar number of my own projects, e.g. https://git.nzoss.nz/lightweight).
Here's a case study for a specific app that might be of interest: https://tech.oeru.org/2018-update-oeru-technology-stack#case-study - in effect, I spend an hour a month per service at most doing maintenance, maybe a few hours to a couple days on the set up of the first instance of any given service (subsequent instance benefit from being able to copy my known-good configurations). My OERu Tech Blog site features a bunch of how-tos for setting up some of these services (I need to write more).
Regarding my expertise, yeah, I've had a lot of years of FOSS work under my belt, but nothing that someone who is stubborn and perseveres in the face of tricky problems couldn't replicate, I think.