Drupal 8.x

Hi,
i'm currently an iOS, Javascript developer. I'm not expert level... I would say i'm intermediate level.
I'm now going to develop web sites (not web apps) and i'm exploring various solutions.

I've been considering building a Drupal 8 Intermedia Distribution. The preamble:

Hello Drupal community,

My drupal site sends automatic emails to newly registered users. I was wondering if there is anyway I can have nicer messages be sent to them. For example nice html templates that can be seen on Mail Chimp.

Thanks!

When i uninstall module and than i try install again get error. what can i do?
error is

In twig we can use {{ 'Hello Earth.'|t }} to mark this text as translatable (so i added several of these to my custom twig template). But if i have multiple languages, where can i actually add translation to 'Hello Earth' for other languages? I cannot find it in admin. For example i tried to enable 'Interface Translation' module in MULTILINGUAL section, then i cleared all cache, then i go to Configuration -> User interface translation but i don't see my strings in the list! Please help!

Is there an upgrade path from Drupal 6 node reference fields, to entities as used in Drupal 7 and 8?

I have several Drupal 6 sites using Node Reference CCK fields. The D7 References module "integrates with the content_migrate module present in CCK 7.x-2.x-dev to allow the migration of field definitions and field values from D6".

But D7 (Entity reference) and D8 (Entities in core) make use of Entities. How do I upgrade?