Managing multiple WordPress sites for clients is a solved problem -- but the solution depends on how many sites you manage and what your actual bottleneck is.
I've used all three approaches. Here's when each one makes sense.
The three real options
ManageWP -- cloud-hosted dashboard, monthly subscription (~$2/site or $100+/month flat), handles updates, backups, uptime, performance checks. Polished UI.
MainWP -- self-hosted on your own WordPress install, free core, paid extensions for advanced features. You own the data.
