Upgrade CI3 to CI4, ORM, other...

Answer to #2: Using an ORM is the perfect solution if the ORM is a good one

What is a good ORM? it is an ORM that relies on the principle:
"It's not the ORM that drives the design of the database but the opposite"

For example, in some ORMs, you can't have a many-to-many association, instead, you have to create an extra Entity, which is very bad because the resulting database is not the one that you want.

A good ORM only offers advantages:

• the design of the database is the one that you want
  
• you can make some raw SQL queries
  
• and obviously, you benefit from the power of the ORM: it automatically creates objects from the database
  

This is why I've created an ORM for CI 3.1.10 and you can find it on GitHub: https://github.com/vmoulin78/concorde
and the website is: https://www.concorde-project.org