Central Craft CMS management for agencies
To your first problem there is a plugin to handle Single-Sign-On here: https://plugins.craftcms.com/saml-sp I've used it successfully with Azure AD, it will be expensive for 60 sites, but perhaps it's worth talking to flipbox factory

On the updates side, there is a plugin that will notify you by slack or e-mail when something needs updating: https://github.com/lukeyouell/craft-updatechecker