Idea for set up structure

setup.php

<?php

namespace themename\setup;
//todo: abstract actual values to another object and pass it to this contructor
class MainThemeSetupMaster
{
    private $cssSetup;
    private $jsSetup;
    public function __construct()
    {
        $this->cssSetup = new CssSetup();
        $this->jsSetup = new ScriptSetup();
    }
    public function initScripts()
    {
        $this->cssSetup->init();
        $this->jsSetup->init();
    }
}

class CssSetup
{
    public function init()
    {
        // call privates
        add_action( 'wp_enqueue_scripts',
            function ()
            {
                $this->_theme_styles();
            });
        add_action( 'wp_enqueue_scripts',
            function ()
            {
                $this->_vendor_styles();
            });

    }
    private function _theme_styles()
    {
        // queue theme styles
        
    }
    private function _vendor_styles()
    {
        // queue vendor styles
    }
}
class ScriptSetup
{
    public function init()
    {
        // call privates
        add_action( 'wp_enqueue_scripts',
            function ()
            {
                $this->_theme_scripts();
            });
        add_action( 'wp_enqueue_scripts',
            function ()
            {
                $this->_vendor_scripts();
            });

    }
    private function _theme_scripts()
    {
        // queue theme scripts
    }
    private function _vendor_scripts()
    {
        // queue vendor scripts
    }
}

Thinking of having one main set up class that can be called like:

require_once( theme_lib . '/setup.php');

$mainSetupInstance = new themename\setup\MainThemeSetupMaster();
$mainSetupInstance->initScripts();

I would then just add other functions like initPlugins() or whatever.

Am I on the right track or is there better way?

Looks good.

One thing I'd probably do slightly different is start with all of those classes being just one class that handles all the CSS/JS/etc. and then only split them out into different classes if they become too complex. Otherwise you have to switch context a lot between the different classes. If you do that, you'll find that it cuts the size of the current file at least in half.

Cool thanks. I am going to refactor it.