Performance on same server: multisite vs multiple single installations

That’s a difficult question to answer without knowing a lot more about the sizes and uses of the sites and whether they would play well together in one installation. When you have many similar sites with similar purpose, content, function and design, multisite can perform well. You can certainly preserve space as well as maintenance effort if you have only one set of themes, plugins, etc.

If you’re a developer trying to consolidate a lot of unrelated things in one place to make them easier to manage, it can become a nightmare. A tool such as InfiniteWP or ManageWP may be a better solution. They wouldn’t change performance or affect server resources.

If you haven’t read this yet, you may want to check out https://premium.wpmudev.org/blog/ultimate-guide-multisite/, which I hope will help you assess whether multisite is a good fit for your sites.