Can I have your email “marketing” advice?

I started my personal newsletter in November 2015. Results are amazing with 10k+ subscribers and 50% open rate but I want to learn from the best in the world and make it even better.

I would love to have your advice and will dedicate my Facebook live today (at http://facebook.com/loic ) at 11h30 PST to email newsletter “marketing” and your tips. Would love your advice during the live and/or in the comments here.

Here is what comes to mind:

• I have 50% open rate. Great. What do I do with the 50% that don’t open the emails. Delete them? Email them to understand why? Ask them feedback?
• I am sending an email every week or so, I would also like to do a “high frequency” list by creating a group interested in getting emails more like every day. No idea how to do this on MailChimp, can anyone help?
• What’s the best practice for design templates? No design? Text only? Mine looks like crap.
• How to avoid spam folders and “crap” tabs on gmail? Been trying a few things.
• Should I write more about just one topic or more like the update in general of what happened last week / my agenda?
• How to coordinate email newsletters with the daily live on Facebook and social networks?
• What to do with other lists (LinkedIn, email contacts etc). I never imported anyone manually in my list.

What else should I learn? What should I do that I am not doing?

Thanks!

update:
video of the live conversation
notes taken in the group (open to all)