Upgrading Drupal

Recently I inherited one very old and outdated durpal6-site and I have to "revive" it. I'm looking at it, and honestly do not know what to do. It is some old D6-site, with 6.28 core and ~50 equally outdated modules. I think first step is to bring it to the latest 6x version, then I will try to upgrade it to 7x.

Q1: Should I start first with core, then modules? Or first modules, then core?

Q2: Can I upgrade core/modules right to the latest version (core to 6.38), or I have to go over all versions in between?

I am getting 'website encountered unexpected error' after update to 7.5 from 7.43. Update returned this error:

Hello,
after upgrading to drupal 7.50 I have solved warning about missing modules but when I go to give the run updates command to update doesn't work so i cannot update.

can you help me?

Not sure where the best forum is for this, I apologize if this is the wrong place.

Are there problems withe the 8.1.8 update? First time I've had any issues with a simple Drupal 8 update. And why does drupal.org continue to show 8.1.7 released on the home page with no update? Keep getting
"Not present
Your sites/default/settings.php file must define the $config_directories variable as an array containing the names of directories in which configuration files can be found. It must contain a sync key."
Been trying a bunch of stuff and can't seem to find what's going on. A little disconcerting.

Man is so frustrating to try to deal with Drupal upgrade but I keep trying :-)

I need to import the config files from D8v1.8 to D8 v2.dev

A) I have a live D6 with the latest data
B) I have a D8v1.8 migrate from an older D6 with my configuration information
C) I have D8v2.dev migrated from the latest D6

I want to accomplish:
1) bring in the latest nodes from my D6 live site to D8v2.dev
2) Import the config information from my D8v1.8 to my D8v2.dev