Hi Ilario,
Greetings!,
There is no impossible task for me in PrestaShop. I am very much capable to modify, building new module, layout modify even I am capable to modify the core of PrestaShop.
I understand your project description and issues. I am very much capable to fixed them for you with very authentic PrestaShop guide line.
Please let me know others 4/5 fixing task. I will care them.
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I think I will be able to make you happy as you afraid from your previous developer.
Kind Regards,
Ranju