Hi,
1. You'll want to change the code:
<a href="<?php echo hikashop_completeLink('product&task=contact&cid=' . (int)$this->element->product_id . $this->url_itemid); ?>" class="<?php echo $css_button; ?>"><?php
to:
<a href="<?php echo hikashop_completeLink('product&task=contact&cid=' . (int)$this->element->product_id . $this->url_itemid).'?return_url='.urlencode(hikashop_currentURL()); ?>" class="<?php echo $css_button; ?>"><?php
in the file "show_default" via the menu Display>Views.
2. For the other changes, you can edit the file "contact" of the view "product" via the menu Display>Views and apply the changes you want to the view. It's just some copy/paste of the code so it should be easy.