Hi,
In the HikaShop options of your products/categories listing menus/modules, you can define how you want to display them. There are already 6/7 different layouts included in HikaShop. You can also change the colors and some other options.
With just the options and some CSS, you can already do a lot to customize the display.
If you want to go further, you can also customize all the views of HikaShop via the menu Display->Views.
The modifications will be saved as template override and you won't loose them when you update.
Regarding templates for HikaShop, you can use pretty much any template made for joomla. There is a company who started to make templates for HikaShop there:
www.websitetemplates.bz/hikashop-templates.html