Okay, will try to explain in more details in our theme documentation.
Don’t worry about PHP notices, they are absolutely harmless, and we will fix them in the next update.
About special symbol in the product name, could you try to use ‘x’ character instead of special char? It will solve the problem. Other way you need to edit our js/functions.js file and remove the following line from there
.replace(/&/g, '&'). To see the changes you need to disable including minified JS in Theme Settings -> Performance.