Hi,
1. This inidicates that the thumbnails for the image couldn't be generated. It probably is because of the permissions of the folders in media/com_hikashop/upload on your server. Make sure that the apache user has writing access to them on your server.
2. Turning joomla caching is not a good idea and actually, if you look at the report from yslow on your link, it tells you what you should do:
Add Expires headers
Make fewer HTTP requests
Use a Content Delivery Network (CDN)
Use cookie-free domains
Reduce the number of DOM elements
None of them are related to changing something in HikaShop or activating the Joomla cache.
3. I indeed already explained you several times what to do by email. I'm sorry but I can't keep answering always the same questions which are even not part of the normal support we provide... After several hundred of messages of CSS and layout customization, I believe I already did my fair share of help to you. Just read the emails where I already gave you the solution to that or ask a designer to help you with styling your shop.