@jiu-cai : The font size can be changed with additional css. Please upgrade to simple catch pro to change font type for different locations, the option to change fonts is available in pro version from customizer.
Please search for an appropriate plugin in plugin directory.
To remove the space in the right side of the menu: Go to Appearance => Customize => Additional css and add the following css
#menu-menu-1 {
display: table;
width: 100%;
}
#menu-menu-1 > li {
display: table-cell;
}
#menu-menu-1 > li > a {
display: block;
text-align: center;
}
#access ul#menu-menu-1 > li,
#access ul#menu-menu-1 > li a {
float: none;
}
Let me know if you need further assistance.
Regards,
Tikaram