Looking for advice on user onboarding with product update emails?

Loads of questions on my mind at the moment:

-- are product update emails a good way to communicate with my signed-up users?

-- how often should emails like this be sent out?

-- what should an ideal product update email include?

-- is DRIP a good tool to use for this kind of emails?

-- cool ideas for a sub-domain to send these from? (tech.insiite.com, updates.insiite.com, product.insiite.com -- how do these sound?)

-- does the looming GDPR mean that I need opt-in for this kind of product update emails?

Here's a little background on my situation and why I am asking this question.

I have recently launched Insiite, a tool for organizing online research. You can basically clip web-pages and PDFs and then make annotations. Highlights can be labeled which means that you can pull together all your highlights with the click of a button -- https://insiite.com

I've been pretty active on Twitter and am starting to see a slow stream of new users signing up to try the service.

Users aren't doing very much once they sign up so I'm experimenting with a number of things to increase activity from new users.

Last week I put together this short explainer video and it seems to have helped get some users a little closer to that magic 'WOW' moment -- https://www.youtube.com/watch?v=7OVqOUIp8SM

I have Reamaze installed and I've seen quite a large number of users click this to try and access the support documents (which are mostly non-existent content at the moment). That's my main focus this week to get more of these finished.

I've tried reaching out to users with an email, but haven't seen any significant success with that yet. Here's an IH post talking about the template that I have been using for my welcome email -- https://www.indiehackers.com/forum/why-isnt-anyone-responding-to-my-welcome-email-39a811cb59

We are still finishing and putting out new features every week. This is especially true for the web clipper, as enabling it to neatly clip a new style of web-page means that product updates are pretty frequent.

I keep stumbling on the suggestion of product update emails and initially this does feel like a good fit for our product.