Hi.
About missing icons in submenu, you could try tip from Helix documenation. In your case add also that lines:
.sp-megamenu-parent .sp-dropdown .sp-dropdown-items .sp-has-child > a::after {
font-family: "Font Awesome 5 Free";
font-weight: bold;}
About Bottom Arrows use
[class^="icon-"]::before, [class*=" icon-"]::before {
font-family: "Font Awesome 5 Free"; }
Helix Troubleshooting Guide is very useful in many cases: https://www.joomshaper.com/documentation/helix-framework/troubleshooting-faq#megamenu-without-arrow-icons-for-submenu-items