So, here are my tips:
+ Don't run an instance for people or a community you don't know.
+ Don't run an instance if you don't have admin experience yourself and don't have a motivated and experienced friend who wants to run the instance together with you.
+ Don't run multiple instances.
+ Don't run an instance for more than 100 people if you are a single admin without admin experience. (If you still think it is a good idea. And a single user instance can be a good idea, for example.)
+ Don't run an instance for more than 1000 people if you are a single admin with admin experience.
+ Don't run an instance for more than 10.000 people. Just don't. You can't handle it if you are not planning to employ people full time.
If you want to run an instance for a community with more than 100 people, pick a good and motivate friend to help you. Find someone you trust to help. Someone you trust in helping you do the ugly decisions that will come.