Hi,
Your current request is for high customization and that's not something that our support forum can provide.
More than that, your question is pretty vague and it is really hard to give you an advice.
All I can tell you is that you can have access to all images in a product page, so it's up to you to make the javascript to generate some kind of lightbox gallery.
"Squeezebox" is provided by Joomla itself and you can use a little javascript script to close the "current" popup.
With the new Cart/Checkout system in HikaShop 3 ; you would be easier for you to manage the "add to cart" because it could be done using ajax.
With the current version (or an old version like HikaShop 2.2.2) you should be able to use the "return url" with the add to cart ; to redirect the user to a specific page, which will just close the popup.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.