I've never seen them advertising anything besides ICOs before as well but I assumed It's because that's what the majority of people do now, I doubt they'll deny my application just because of that.
The former gets you quite a lot of views and readers, the latter probably less so, but actually with the market in this downtrend, there are far fewer projects advertising this way than they were months ago, so you might actually get higher visibility now.
Signature campaigns with good members? That's really good visibility for active forum users (who are, presumably who you want to target).
Have any links where I could start when it comes to the newsletters/press releases?
The product is not really going to be profitable and It will also be open source so I'm not sure I could keep up with a signature campaign.