QUOTE:  Each piece of duplication in your on-page SEO strategy is ***at best*** wasted opportunity. Worse yet, if you are aggressive with aligning your on page heading, your page title, and your internal + external link anchor text the page becomes more likely to get filtered out of the search results (which is quite common in some aggressive spaces). Aaron Wall, 2009

Early versions of search algorithms relied on webmaster-provided information such as the keyword meta tag or index files in engines like ALIWEB. Meta tags provide a guide to each page's content. Using metadata to index pages was found to be less than reliable, however, because the webmaster's choice of keywords in the meta tag could potentially be an inaccurate representation of the site's actual content. Inaccurate, incomplete, and inconsistent data in meta tags could and did cause pages to rank for irrelevant searches.[10][dubious – discuss] Web content providers also manipulated some attributes within the HTML source of a page in an attempt to rank well in search engines.[11] By 1997, search engine designers recognized that webmasters were making efforts to rank well in their search engine, and that some webmasters were even manipulating their rankings in search results by stuffing pages with excessive or irrelevant keywords. Early search engines, such as Altavista and Infoseek, adjusted their algorithms to prevent webmasters from manipulating rankings.[12]

I’ve got by, by thinking external links to other sites should probably be on single pages deeper in your site architecture, with the pages receiving all your Google Juice once it’s been “soaked up” by the higher pages in your site structure (the home page, your category pages). This tactic is old school but I still follow it. I don’t need to think you need to worry about that, too much, in 2019.
If you don't know the difference between head terms and long-tail keywords, let me explain. Head terms are keywords phrases that are generally shorter and more generic -- they're typically just one to three words in length, depending on who you talk to. Long-tail keywords, on the other hand, are longer keyword phrases usually containing three or more words.
QUOTE: “For the mostpart it should be fine I think the the tricky part that you need to be careful about is more around doorway pages in the sense that if all of these pages end up with the same business then that can look a lot like a doorway page but like just focusing on the content duplication part that’s something that for the most part is fine what will happen there is will index all of these pages separately because from  from a kind of holistic point of view these pages are unique they have unique content on them they might have like chunks of text on them which are duplicated but on their own these pages are unique so we’ll index them separately and in the search results when someone is searching for something generic and we don’t know which of these pages are the best ones we’ll pick one of these pages and show that to the user and filter out the other variations of that that page so for example if someone in Ireland is just looking for dental bridges and you have a bunch of different pages for different kind of clinics that offer the service and probably will pick one of those pages and show those in the search results and filter out the other ones.
Many think that Google won’t allow new websites to rank well for competitive terms until the web address “ages” and acquires “trust” in Google – I think this depends on the quality of the incoming links. Sometimes your site will rank high for a while then disappears for months. A “honeymoon period” to give you a taste of Google traffic, perhaps, or a period to better gauge your website quality from an actual user perspective.

Google WILL classify your site when it crawls and indexes your site – and this classification can have a DRASTIC effect on your rankings. It’s important for Google to work out WHAT YOUR ULTIMATE INTENT IS – do you want to be classified as a thin affiliate site made ‘just for Google’, a domain holding page or a small business website with a real purpose? Ensure you don’t confuse Google in any way by being explicit with all the signals you can – to show on your website you are a real business, and your INTENT is genuine – and even more important today – FOCUSED ON SATISFYING A VISITOR.
For example, let’s say you were running the website of an online pet store. You might be wise to create one keyword grouping for all your dog-related products, then one for all of your parakeet-related projects, etc. The next step would be to segment each individual group into smaller subgroups (parakeet cages, parakeet toys, parakeet snacks) and then even smaller groups for each type of product (low-fat parakeet snacks, luxury parakeet snacks… you get the idea). Now your pet store can create individual pages optimized for each small keyword group.