You’ll need a more sophisticated setup than that, these platforms track everything from useragent to fingerprint/cookies. If you leak one of those across your botnet of accounts it’ll flag not only your botnet but might flag your streams as well.
Using 500 free Spotify accounts manually presents a risk of detection, though it's lower than with bots. Free account activity patterns can appear predictable and trigger Spotify’s anti-manipulation systems; diversifying listening habits beyond just your songs is good but consistent behavior across all accounts could still raise flags. Consider supplementing this with genuine listeners or exploring more sustainable promotion methods to avoid potential penalties.