Drupal 8.x

In my mind Drupal 8.8.8 is the current stable release of Drupal 8.x and 9.0.1 is the next stable branch, Drupal 9.x.... but what the heck is 8.9.1, a transitional step in between 8 & 9?

Not only am I new to Drupal but I am brand new to making websites or any coding. The NGO I volunteer for was desperate and got me, so I appreciate your patience.  We are about 80% sure we want to use Drupal 9/8 but want to make sure we can do it.

Aside from my lack of expertise, our main limitation is money and hardware.  I only have two 2GHz 4GB RAM laptops with one standard ethernet connection.  I have read what seemed to be the most similar posts but still am not clear on a few things.  My specific questions:

OK, I can get Joomla, PHP fusion, glfusion, Wordpress, B2Evolution, etc, But Drupal, Its a complete Mess.

Ive installed Full Calendar, the instructions are a complete mess, I installed another Calendar and I'm missing dependencies. And another one (I forget its name)

Does Drupal have a GOOD Calendar/Agenda system? If I can AT LEAST Get that, I will muddle through the rest of Drupal.
I need a Calendar/agenda with good instructions (Ive read a ton of instructions) and a way to make a menu. I figured out how to do it with Forums but everything I am flying blind on.

For my Drupal 9 site, phpmailer is not yet available, so I have used swiftmailer + mailsystem. But I cannot find any place to enter my credentials. Do I need another module?

Thanks for the help,

Jim

I am trying to figure out why something weird is happening. I have the following in my_module.routing.yml:

my_module.test:
  path: '/my-module/test'
  defaults:
    _controller: '\Drupal\my_module\Controller\TestController::view'
    _title_callback: '\Drupal\my_module\Controller\TestController::getTitle'
  requirements:
    _permission: 'access content'

My Controller class is this:

Hey, there!

Is it always necessary to do a dependency injection for a service within a class if we will only use that service once inside the class? According to the Drupal documentation, is that recommended, but for practical purposes, is that useful?