Hi,
1. The show select option is a good idea. But if you want to display the price per weight using another unit than the one selected in the product weight unit selector, that would require some code customization in the product / listing_price.php view file via the menu Display>Views.
2. Regarding the "per unit", you can implement the solution proposed in "I sell packed products, how can I change "each" text in the product page ?" section of the FAQ:
www.hikashop.com/support/documentation/106-faq.html