First dokku deploy

I have an express app (based on kyt-starter-universal) with postgresql database and I struggle to figure it out. Setting up Debian 8.6 and installing dokku was easy. After that:

sudo dokku plugin:install https://github.com/dokku/dokku-postgres.git postgres
dokku apps:create myapp
dokku postgres:create myapp-db
dokku postgres:link myapp-db myapp

And then I’m kinda lost. I need to dump sql data to my app container, so executed locally:

pg_dump -U postgres -Fc localapp-db > database.dump

Do I need to grant any privileges in advance to be able access it, like:

GRANT ALL PRIVILEGES ON DATABASE localapp-db TO dokku;

Next step: uploading it to my cloud and executed:

dokku postgres:import myapp-db < database.dump

Here things got ugly - it showed me bunch of errors and failed (hence my question about privileges). Tried it second time - no errors. I tried to check my db, but my knowledge only works to this point. Tried dokku postgres:expose myapp-db but I was unable to figure out how to connect from my local pgAdmin3 installation.

I’m not sure how to set my local app config. From this tutorial: I assume I need to use process.env.DATABASE_URL?

Actual deploying is also a mystery to me. For example using public folder: AFAIK after pushing my git project do dokku container it will execute npm start to build and start my app. But I am supposed to have user uploaded files there, how to ensure they won’t be lost on next deploy? Can I browse its content from the container?

Bonus: I still don’t have a domain name, when I’m setting dokku/nginx can I use the hostname I am supposed to have later (myapp-example.com), or I have to configure it later?

Sorry, this question is too long, but I am kinda frustrated after few days of failures.