Codeigniter beginner questions, going to start learning

hi all,
i am from Oracle Forms/Reports and Oracle Apex, so 
1) what are the challanges for me to start coding using Codeigniter? 
and
2) where and how to start? what are recommendations from seniors?
3) the learning material with practical examples, where i can find it? i knew about official site Official User Guide
4) recommended vs code extensions specifically for Codeigniter / PHP / HTML 5 / CSS 3 to code fast and save time
5) please recommend to start with version 3 or 4
hope i can learn and start coding asap with your help. 
regards

If your starting out then learn CodeIgniter 4.
CodeIgniter 4 Development
IncludeBerr CodeIgniter 4 Tutorials.
Nice tutorials - IncludeBeer

What did you Try? What did you Get? What did you Expect?

Joined CodeIgniter Community 2009.  ( Skype: insitfx )

thank you for help @InsiteFX
downloaded CI 4 and will follow this tutorial.
regards

Try the official tutorial, if you didn't do it.

Build Your First Application
https://codeigniter4.github.io/userguide...index.html

ci-phpunit-test | CodeIgniter Testing Guide | CodeIgniter 3 to 4 Upgrade Helper

thanks @kenjis , already following this guide.