There is no limit on the number of templates but it will be cumbersome to manage 100 templates.
That said, I would recommend finding the components/widgets that remain the same across templates and the ones that change. Then create a master template with some dynamic components that can be changed as per the site requirement. In other words, Have components that change based on the site instead of template.
EX: Keep the footer and header as static component for all templates and choose other components as Dynamic