Hello,
01. You can use a WooCommerce Variable Product: create an attribute with your 3 options, enable it for variations, then set a separate price for each variation. Each dropdown selection will automatically show its corresponding price: https://woocommerce.com/document/variable-product/
If you want to show drop-down instead of swatches, disable the swatches from Product > Attributes > configure term.
02. Navigate to Theme Settings > Single Product > Tabs and choose the tabs layout “Accordion”.
03. Try to create a custom layout for a single product page and add the size guide widget where you want to show.
Here is our documentation on how to use Layouts in our theme: https://xtemos.com/docs-topic/woodmart-woocommerce-layout-builder/
04. Could you please elaborate on your concern more with some useful screenshots so that we can better understand and assist you accordingly?
Also, share your Site WP-ADMIN Login details in the Private Content field so that we can check this concern on your Site and help you out accordingly.
Best Regards,