Where can I spend my ingame currency? I can't find a shop anywhere

[Moxder]

I just bought the game, where can I unlock more songs? (except buying DLC)

[Luky]

There used to be a pop-up bar in the bottom, which led to a shop, where you could buy more profiles, banners and song packs (with the ARKK currency). But since 0.3.001 EA, that's been removed.

It's not possible for now. There's a lot of features that had to be temporarily removed due to the changes in the game. Everything will get added back eventually at some point.