Hello,
1) That row is custom development. But you can create something similar using Static Blocks and Header widget area.
For example, go to Elementor settings and enable that for the static blocks https://xstore.helpscoutdocs.com/article/47-static-blocks
After that create a header static block with the content you need (for example red row with the sale bg image with the texts and button inside).
Then go to Appearance > Widgets > add the Static block to the Header banner widget area. Then go to Theme Options > Header builder > Widgets > Position Of Header Banner Widget Area > Above the header.
3) In Theme Options > Styles > you can change the colors of all the buttons on your site.
In Theme Options > WooCommerce > Single product builder > Back
Add to cart & quantity > manage the Add to cart and Buy now buttons only.
4) Don’t see problems with that https://gyazo.com/6e6ff1e0356f62d88f0d8b814e9847b4
5) Theme Options > WooCommerce > Shop Elements > Sale & Out of Stock & New settings.
Regards