Hello!
For your first issue, try turning on Quick Shop in your theme options. It seems the theme may be requiring the quick shop to be enabled.
For your sale prices, it looks like the theme supports ranges. Generally, this is something built into the theme. You’d likely need some custom code in order to show a + rather than a range when you have a range of prices on variants. You can check section settings in admin when customizing the theme on product pages to see if theres an option to change this display.
Hope this helps!