The problem is where to go, tastes varying so widely. Most of our favorite restaurants have recommended on site--primarily from store clerks and hotel staff.
I would not plan everything now. If you download the Fork app, you can make reservations closer to the time you are there. It works just like OpenTable in the US. Or if a place looks good to you in your wanderings, ask for a reservation there later in the evening.
Making reservations places you above "ordinary tourist". It shows you have an interest in the restaurant and are actually thinking about your dining experience. It can affect your dining experience. That said, we often make reservations at lunchtime for dinner that evening. Depends on how popular the restaurant is and how big. A number of the places we frequent only have 12 tables so reservations are important. With some I make the reservation a week ahead.
I have yet to have a different dining experience with no reservation than with one. Not sure where that happens but so far, so good.
If you have favorite places, book ahead.
I am in Rome now and booked my favorite place as it is open on Sunday when others are not and without a reservation, could miss out but I do it just days before. And I have booked only one other, the other days, just walked into somewhere that looked to me.
The Fork works great but they do not all use that facility. I had to call when I reserved the other restaurant.
Have a good trip