It does seems that Mylio would work well for you. There’s a few ways you could use your current devices to setup a self-sustaining Mylio environment. I’ll try to answer your specific questions, but there’s more than one way you could set up things depending on your preferences.
What would be your suggestion on how to setup Mylio for me, to use the app as DAM for all my pictures from local drive and iPhone?
There’s two ways you could go about adding your media. One consideration that might narrow that down is whether duplicates photos might exist between your two sources (phone and hard drive). Or even if duplicates might exist within the hard drive itself. If the answer is yes to the dupes question, then I recommend you set either your NAS or an external drive as a Vault, then add your phone and sync its photos, then do a COPY import of the directories in your external drive with all the media in it. This will create an automatic copy of all your Originals in the Vault (NAS or Drive), and it will give you the option to exclude Dupes from being imported.
If duplicates is not a concern, you could choose the option to “Add without moving” all the files in your external drive. This will catalog all the content int hat drive and turn the drive into a Vault (which mean new content you add to your library will automatically go to that drive also).
Either option will preserve your existing organization and folder structure. The photos from your phone will go to a new, separate folder names after your device type.
I’d suggest you have at least two vaults set up in Mylio. Depending on how your existing backup mechanism works, you might want to keep it or you might want to let Mylio do it all. You can add multiple drives, your NAS and a cloud based vault and Mylio will keep them all in-sync. You can find out more about the mechanics of adding each device type here: Adding Additional Devices.
You simply open the Mylio app on the devices you want to sync (or the device that hosts your storage, like the computer that host the NAS or that the drives are connected to), and Mylio just adds any new files automatically. This is true for photos that you take with your phone, or for files that your copy to a folder that Mylio is aware of (Import with Source Folders - Mylio) - Otherwise, you manually import new content to your Mylio library and that will get sync’d everywhere.
There’s weekly webinars that cover getting started and how to go about the process. You can register for them here: Webinars - Mylio
Feel free to ping me here if you have specific questions or contact our support team at firstname.lastname@example.org