On Instagram, you can't totally hide your followers, but you can change your account to Private so that only authorized users can see them. You can also remove followers or block particular users if you don't want them to see your list of followers.
You can modify your display name at any time by opening Spotify, going to your profile, and then tapping or clicking on it. However, keep in mind that your Spotify username is fixed and cannot be altered, so only the display name will change.
You can simply uninstall the Snapchat app from your phone, or if you want to completely stop using it, you can delete your Snapchat account by going to their manage account section.