Can you try this?
@media
(-webkit-min-device-pixel-ratio: 2),
(min-resolution: 192dpi) {
#site-logo {
margin-bottom: 20px; /* Change this value to suit your needs - will impact both iPad and iPhone */
}
}
Will get back to you on the other queries in few hours time. Also, pls consider that you may not require go-to-top button iOS devices at least since touching the top bar takes you to the top. I use this all the time. Not sure such an option exists in Android though.