Upgrading Drupal

Hello,

I am relatively new to Drupal so this could definitely be a user error. I am trying to update Drupal Core from version 8.3.7 to 8.4.0. I am currently hosting Drupal through 1&1 and utilizing FileZilla to access my database via FTP.

After attempting this update twice, I still see the following:

1) No pending updates when visiting website.com/update.php
2) Updates available under Extend Tab --> Drupal Core 8.3.7 to 8.4.0

Below are the steps I followed but still seem to have no luck in updating this core correctly:

Drupal Core update is my least favorite part of my job. This is not a process I do frequently, so when it does come up for an update, its always a huge mess. Has anyone developed, or come across, an easy, general step by step for the process? I have gone thru a run thru with our Web designer, but I still can not make heads or tails of it.

Upgrading requires running update.php which updates the database. But here is where I was fooled.

You usually put the site in Maintenance mode. Install your new stuff. The site still continues to show the Maintenance Mode default page. Then you would look at a Report of the Status and that would tell you if the database needed update (at least half the time it does not). Then you update the database if needed.

Enocured site problems message before plain update to Drupal 4.3.6 to newest.

Some pages can be opened - some with errors.

I was backup files on time before update but now site is down with message about encored error on every page I was open.
Seems, problem associated with DB.

p.s.: after every update I do I have problem with views module. It's broken every time and I need to reinstall in and recreate blocks manually.

Whats about Drupal stability? It's horror.

I have a drupal 8.3 installed with composer
When i try to update core to 8.4 with : composer update drupal/core --with-dependencies
he told me everythings is up to date.
when i look into composer.json :
"drupal/core": "~8.0",
"drush/drush": "~8.0",

I have drush 8.1.14 installed so i try to changed composer.json with :
"drupal/core": "~8.4",
"drush/drush": "~8.1.14",

then run composer update drupal/core --with-dependencies
but nothing happened, ssh is blocked.

I see just after updating the drupal 8.4 readme which tell us to not update width old version of drush.....
So I has an old version and now the site is off....
Fatal error: Interface 'CommerceGuys\Intl\Currency\CurrencyInterface' not found in /home/fournilencevenne/public_html/modules/commerce/modules/price/src/Entity/CurrencyInterface.php on line 16
Drush command terminated abnormally due to an unrecoverable error. [error]
Error: Interface 'CommerceGuys\Intl\Currency\CurrencyInterface' not
found in