Hey there, if you haven't updated your new R5s firmware to the current version do that first (find the R5 settings cog by either pulling down the shade while in the R5 home page, or pulling up to show all apps, tap the cog. Scroll right to the bottom to "System", tap "Wireless update" and allow the R5 to update itself (this is an iterative process, so you may have to perform this several times to reach the current version which will finally tell you that your firmware is up to date and no further update is available).
The card setup is really very simple and just requires you to put the card in the R5 (the card will be formatted in the required manner automatically by the R5 as external memory), install Spotify from the play store.
Open Spotify, then tap the Spotify Settings icon (also a cog, in the top right of display), scroll right down to the bottom of all the options, and you will see (One up from the bottom) "Storage", tap that, and once in choose "SD card" and that's it.
I only have a 256GB card, so I can't say with absolute certainty that your 512GB will work, but I'd be very surprised if it didn't!
Welcome, and enjoy your R5, it's a great little DAP