before you configure wordpress multisite, answer one thing honestly: will these sites ever need different plugins? if the answer is yes, even slightly, stop there. the next few years are network activated plugins and per site overrides and you will not enjoy them.
i run one network of nine sites that are genuinely identical. same theme, same six plugins, only the content differs. it is lovely. one update run, one backup job, one ssh session. the two networks i inherited from other people were both the wrong shape: an agency that put unrelated client sites together to save on hosting, and a company that made every regional office a subsite and then let each office choose its own form plugin.
practical things the tutorials leave out. subdirectory versus subdomain is close to permanent, so decide it with the dns in front of you rather than the theme. domain mapping is in core, ignore any guide telling you to install a plugin for it. a plugin that is not multisite aware will happily write to the wrong table and you will not find out for weeks. and the big one, a single fatal in a network activated plugin takes every site down at once, so the rollback plan matters far more than it does on a standalone install.
getting out is worse than getting in, too. pulling one subsite into its own install is an afternoon with wp-cli if you are lucky, and a week if the plugin data is keyed by blog id.
how big is the largest network you have had to look after, and did you regret it?
Source: r/WordPressToolkit · by /u/rubenriis