While Bubble enables you to do many things, my recommendation is to build for simplicity first. As you validate your initial idea, then you can build additional complexity (ex. sub-domains) later on. (Sub apps and working with the API connector are great tools, but only once you have a well-established base product).
While ever situation is different, in most cases you should be able to easily and readily accomplish what you want to do with Option 1: build one app and filter views. Proper page-level redirects and database privacy roles should take you a long way. (For more context, I recommend viewing this post: How can a user only see his own data saved not others).