KafleG

Hello,
There are lots of WordPress theme available for Music purpose. But fist you have to be clear about the type of theme you need with features. Please visit the Link to find the music theme as your need. More theme related to music and musician are also available here. Please find the perfect theme for you. If exact need is not provided by the theme, you have to do some custom work for it. If you need more help, feel free to ask.
Thanks

Hello,
Would you please provide the link of your site? Are you using any plugin for social sharing for that page or using theme default sharing feature? Let me know the reality about it, so that it help me to address the problem easier.
Thanks

Hello,
There is no any options to add header image on this theme. Would you please elaborate your question how you add header image? Please provide the link of your site and i will try to find the issues in simple way.
Thanks

Hello,
Please add the below css code on Custom Css manager to change the color of scrollbar.

.nicescroll-cursors {
    background-color: red !important;
}

Please name the color as your need.
Thanks

Hello,
Please remove the CSS code you add above.

.site-logo.attachment-edin-logo{
margin-left: -75px;

This code is making your logo more smaller. So please remove this once and have a look. If not work, let me know.
Thanks

Hello,
Try by adding the below CSS code.

.header-wrapper {
    width: 100%;
}

Note: Child theme is recommended to customize theme.
Thanks

Hello,
Are you using Menu for Social Icons? If so go to screen options and find Open in new tab. Screenshot
Try once, if not work let me know.
Thanks

Hello,
Why are you adding the above CSS code? You want to make the site logo smaller? would you please elaborate your question and make me clear about the issue. I will try my best to help you.
Thanks

Hello,
Try to find the solution on Great theme Documentation or,
Go to Appearance > Widget > and add the slider widget on slider widget area.
Try once and if not work let me know.
Thanks

Hello,
Try by adding the below CSS code

.menu {
    background: indigo !important;
}

.menu > li > a:hover {
    background: red;
}

There are thousands of free plugin available on WordPress plugin repository.

Thanks ??

Hello, You have to find that code on theme files and need to edit this code. If you are unable to find the code or can’t edit the theme try it once by CSS approach. If you are unfamiliar with CSS too, please provide the link of your site, i will provide you the CSS code. If you have any question, please feel free to ask. I will try to help you more.
Thanks

May be instead of putting widget on right sidebar you puts on footer widget. Please verify once by Appearance > Widget
Thanks

Child theme CSS is properly enqueue in functions.php?

Try by installing new and latest WordPress and check your theme there. If not work again, try by using latest PHP version also. This problem may arise due to the permission issue of folder too. Try it. ??
Thanks

would you please provide the link of your site? It help me to address the problem more easier.
Thanks