@Makoto, this is kind of off-topic, but
1) Love this guide, and when I've got enough time set aside to test an upgrade and go through in production, I'm sure this will be super helpful as someone with (very) limited server admin experience (I followed enough guides to get a secure LAMP stack up to run IPB, but that's it). So first off, thanks for taking the time
2) Any chance you would be willing to do a short summary of what a dedicated IPS server might also have installed by way of mariadb (and version), php (and version), any specific thoughts on php functions to disable/enable, which php accelerator to use, etc etc etc. Kind of "hey, once you've followed a guide to setting up a VPS and followed the guides on securing your admin user and getting fail2ban and other recommended stuff installed to make it safe, here's your LEMP stack specifically tuned for IPS 4". That's a big ask, but you seem to be the active admin with tips around here, so figured I'd ask