License Key vs Named User
You are correct. If you don't want your app's user to need an ArcGIS Online or on-premise named user account, then you will need a Runtime License. A single license key is valid for a single user on a single device. License keys are sold in packs.
Basic vs Standard
It depends on what your workflow is.
- Basic: If you are using one of the in-built workflows for editing, taking the data offline and synchronizing using ArcGIS feature services with either the OfflineMapTask or the GenerateGeodatabaseTask (which make use of mobile geodatabases), then the Basic License will suffice. It does include editing capabilities. If this is what you were referring to in your original question, Basic is the right license for you.
- Standard: If you are building your own editing workflow that relies on something called a "File Geodatabase", perhaps generated by ArcGIS Desktop, then you will need to do a fair bit of work as we don't currently provide workflows for this. And at that point, to access the File Geodatabase, you would need Standard.
Note also that if you are just editing data stored in a completely public ArcGIS feature service (i.e. anyone can edit the data with no authentication required), you only need Lite, but that is such a rare use case, it's seldom mentioned.
JS API from the Web
The Lite/Basic/Standard/Advanced Licenses are Runtime specific. For the web, you should use Named Users.
