Converting gulp config to gulp 4

[georgatgalaniprojects]

Hi, I inherited this legacy gulp and gulpconfig files.
Those are pre Gulp 4 and I am trying to convert them to Gulp 4.
I am quite new to Gulp in general so I have some problems figuring out how to convert this. Any hints would be welcome.

gulpfile.js

'use strict';

var gulp = require('gulp');
var gulpConfig = require('./gulpconfig');
var path = require('path');

// Gulp tasks
require('gulp-task-postcss')(gulp, gulpConfig);
require('gulp-task-svg-stack')(gulp, gulpConfig);

gulp.task('default', [
  'postcss',
  'svg-stack'
]);

gulpconfig.js

var path = require('path');

module.exports = {
  basePath: './assets',
  stylesheets: {
    processors: {
      'postcss-mixins': {
        mixinsDir: path.join(__dirname, 'assets', 'postcss', 'mixins')
      },
      'postcss-advanced-variables': {},
      'postcss-color-function': {},
      'postcss-calc': {},
      'postcss-extend': {},
      'postcss-nested': {},
      'postcss-responsive-type': {},
      'postcss-flexbugs-fixes': {},
      'autoprefixer': {
        browsers: ['last 2 versions']
      }
    }
  },
  svgStack: {
    src: path.join('icons', '*.svg'),
    dest: 'images',
    filename: 'iconstack',
    svgSpriteOptions: {
      namespaceClassnames: false
    },
    transform: [
      {
        svgo: {
          plugins: [
            { transformsWithOnePath: true },
            { moveGroupAttrsToElems: false }
          ]
        }
      }
    ]
  },
  stylelint: {
    src: path.join('postcss', '**', '*.p.css')
  },
  notify: {
    successIcon: path.join(__dirname, 'gulp', 'images', 'success.png'),
    failedIcon: path.join(__dirname, 'gulp', 'images', 'failed.png'),
    errorIcon: path.join(__dirname, 'gulp', 'images', 'error.png')
  }
};