I've managed to build up a large following on social media and would like to release an eBook on a certain niche, what are my next steps?

I've spent the last few months growing a brand that now has over 50K followers. There are only a few larger accounts than me that post similar content but at the rate that I have been growing I'm confident I'll be able to become of the larger accounts.My plan is to begin building an eBook that I will sell once I hit 100K. I've already decided that my platform of choice to sell the product will be Gumroad.My question is, what software would be ideal for writing the eBook? I could use Google Suite's like Docs, but I just feel like it wouldn't look too physically appealing. Does anyone have any experience with a power tool that's relatively easy to use?My second question is, let's say I want to refer to research/news articles, scientific papers, or other books that I found online to support my argument. Aside from giving them credit and citing them in a bibliography, is there anything else that I need to do? Since I'm citing these papers and then making money (of course the majority of the eBook will be my own work) I'm just not sure if there are other steps that I need to take (like reaching out to them and asking for permission).My third question is, is this something that should get copyrighted? I'm not sure how that whole process works but I've seen similar eBooks that have gotten copyrighted so I'm just curious.Lastly, I was thinking of collecting emails using MailChimp or Google forms in anticipation of the release and then sending an email out once the book is released with a discount code. I will also be designing promotional material in preparation for the launch. Does this sound like a good idea/is there anything else that I should consider?Thank you for taking the time to read this! see hubwealthy.com/wealthy