Hi RogerSch,
welcome to RuneAudio.
1] When I add the network folder (Synology NAS) where all of my music is stored. Will it be possible to browse through the folder structure or will Rune Audio scan the metadata of the files (FLAC) in the sub-folders and create a library?
Yes you can browse your music by folders.
As an alternative you can also browse by Artist, Album and Genre.
2] Does Rune Audio support multiple libraries?
No
3] How does Rune audio cope with large libraries?
Good, only the first database update takes some time.
Frank