Greetings 
Titles
Suggesting a length of 2-4 words is only viable for a particular area of SEO. That would be if you have a site with a high Domain Authority, as in an established subject expert. In this case you can compete in what's referred to as a broad keyword targeting. For everyone else, including all the "bloggers" here, since you don't have DA your best bet is to target what's known as long tail keywords with your title.
This requires doing keyword research and identifying low hanging fruit, understanding what your competitors are doing, and besting their efforts. To do this would encompass both the title and also a number of other elements such as h1, h2, going after snippets, meta descriptions, internal linking structures, links in and out, and then most importantly HELPFUL CONTENT that's in the area of 1200+ words. More on all that below..
To be honest if you even understand all this, there's still another level deeper on titles that you'll need to go. That would be understanding how to target niche topical subjects using long tail keywords. That is NOT doing broad term long tail but rather more niche topical long tail. Because going back to DA, if you use long tail you cant target broad topics with it because your competitors with more DA will far outrank you. So we start with niche long tail topics, where a piece of quality content stands a chance to out perform your competition.
SEO is a WAR! SERP is a WAR. You are always fighting to best your competition. look at google rankings and see the subjects you want to talk about, and see your competition in the results, analyse them, understand their strengths and weaknesses, then seek and destroy!
SEO is extremely competitive and requires real subject expertise.
Headings
Your headings tips were ok. H1 is for title only, H2 is for secondary titles, I wouldn't bother with h3 unless you're actually serious about all this.
h2's are SEO opportunities, this is where you would attack additional keywords and search terms that you are trying to rank for. The best tip I can probably give here off the top of my head would be to make sure the H2 titles are relevant to the H1 title topic. Dont have an H1 "The Ultimate guide to SEO blogging" and then there's h2's that are completely unrelated, like H2 "Today in splinterlands".. If you really want to put in the work to do this properly use a tool like Also Asked.
Go to the tool and type in your search term that you are targeting to rank for. The tool will spit back an organized list and hierarchical structure of other similar topics that those users are also looking for. In SEO you need to be helpful, that is key, needs to be value add. Google is looking for this, and if you can deliver on your subject plus be helpful for similar topics that are also relevant and useful for that searcher than you're scoring points.
As you are doing article research and again analyzing your competition and forming your content piece I suggest you start with your H1, and 4-5 H2's from a tool like Also Asked or even just using Neil Patels Ubbersuggest and seeing who is currently ranking for your terms, going to their content, seeing what they are doing for H1 and H2's then one upping them at it. I'll leave that there, I don't want too give away to many secrets of the trade. 😜
Images
Some actual tips here would be 1) use image descriptions, this info helps google to rank you against your competition, Again incorporate your keyword or key phrase strategy into the words you use in your description.
A second tip 2) would be to use caching and image compression to speed up load times on image heavy content. But cant do those thing on hive.blog or peakd.
Links
Hate to say but you're incorrect with your advise here.
Outbound links are not such a big deal
They are a big deal, linking is a very big deal both internal and external linking. SEO and SERP specifically is all about establishing Authorty in the eyes of google. For anyone that is actually interested in SEO its worth your time to learn proper link structuring throughout your content and within your website. Content should consist of "Pillar Posts", and "Response posts", and then a third group of more shareable content, and finally your affiliate posts. Pillar posts are your 2,500+ word evergreen posts that cement your foundation as an expert in a particular subject, an Authority. A good link structure might look like this -> response posts that you have ranked for bring traffic in, then internal linking from these response posts link to your authoritative pillar posts.
This structure builds authority and tells google, or actually essentially points google to your authoritative content.
From here you'll want to incorporate external links from your pillar posts to other AUTHORITATIVE domains on the same subject. Link out to websites that have established authority on the subject, this again tells google that you're being helpful, credible, and authoritative. I wish I could explain this properly, this is something that takes many hours of study to fully conceptualize. But please research internal linking structures, and linking out to authoritative sites, this is part of any half decent SEO strategy.
Tags
Including the correct tags will help for content discovery here on hive and peakd, for SERP I would focus on your keyword or rather key phrase strategy and then as you suggested incorporate those keywords as tags.
RE: Help Hive - Sprinkle A Little SEO On Your Posts