PHP/OOP how to design classes for a small project

I need a bit of advice, how to design my PHP classes. It should be a few classes building/re-building a menu for another application.

Initial data:

1. a big json file, menu json chunks are repetitive so we have a global menu

{json data}
[menu_column1]
{json data}
[menu_column2]
{json data}
.....

2. menu item template

{json data}
[menu_item_name]
{json data}
[menu_item_url]
{json data}
[menu_item_id]
{json data}

3. a list of menu items name url id

Note: Cannot edit the menu with original visual editor, due to many menu items, it just get stuck.

I wrote a simple script (around 100 lines of code), that

• opens 3 files
• sorts the menu items (just for printing to screen)
• finds duplicates by name or by url
• resorts menu items horizontally or vertically (4 columns)
• generates json of each menu item - column
• generates the menu json (4 columns).

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I'm trying to build the same into OOP, right way, using patterns where is possible.

At the moment of building classes appeared some questions:

• where and how to store configurations (in my original code have config.php with constants)
• does the input/output need a separate class
• how to operate with files from classes (right way)
• how many classes to create and what is the purpose of each class

Any suggestions how to design my classes would be welcome.