Wordpress site / Product comparator: responsive works, design changes and update for modified plugins

I'm looking for a good developer / designer can carry out some work on a italian Wordpress site, a kind of products comparator with a blog. Below I will list some points, just to give an idea about the objectives to be achieved. Details will be discussed privately. 1) When creating the site, in order to make certain features available, the developers modified the existing plugins. Unfortunately, the developer who initially contributed to the creation of the site is no longer available, so I need help to find out which plugins have been modified, to update them preserving changes made previously. I assume that the modified plugins are at most 2 or 3. 2) Clicking on the images' carousel within the product pages, the lightbox that show all the screens no longer opens. It could be enough update the plugin to solve the problem, but otherwise will need a targeted intervention. 3) I would revamp the blog, because nowadays almost all sites are responsive and adopt a full screen view. In my case the home page and many other pages already seem to be in full screen, but the blogs and articles have edges that greatly restrict the space occupied by the contents. To make a change like that, I think it is also necessary to fix the menu bar, widen them proportionally. The MOZ blog ([login to view URL]) and its articles are a great example of what I aspire to, although I'd like to keep the sidebar on the right. 4) This is the most important and crucial point. I would finally make the site "responsive", to automatically adapt it to any screen. Since this is a site a bit 'special, a kind of comparator products, I'm not sure whether it is better to make responsive the current template or create an ad hoc template for mobile devices, at least for the homepage and the pages regarding the comparison system. The blog can remain the same, as well the "about page" and so on, the important thing is that they are responsive. Regarding the possibility of creating a custom template, privately I'll show an example of what I thought of. I am seeking only professional developers, able to provide an opinion on these points. Thanks for the attention.