how to get limited number of records and order by rand ?

Hi,

I am 100% new to CI 4 and fairly new to MVC.

I did the Build Your First Application and from that I am trying to make my project.

I created a homepage in which I have to load banners and using the example code from news tutorial I got all the banners but I want to get them randomly and also I want to limit the number of banners I get. Right now I am getting all findAll(); so according to this my question is:

1. How to get 5 banners randomly
2. How / Where (in which folder) to add custom js / css and other files ?

Thanks.