I do not obsess about site architecture as much as I used to…. but I always ensure my pages I want to be indexed are all available from a crawl from the home page – and I still emphasise important pages by linking to them where relevant. I always aim to get THE most important exact match anchor text pointing to the page from internal links – but I avoid abusing internals and avoid overtly manipulative internal links that are not grammatically correct, for instance..

Robots.txt is not an appropriate or effective way of blocking sensitive or confidential material. It only instructs well-behaved crawlers that the pages are not for them, but it does not prevent your server from delivering those pages to a browser that requests them. One reason is that search engines could still reference the URLs you block (showing just the URL, no title or snippet) if there happen to be links to those URLs somewhere on the Internet (like referrer logs). Also, non-compliant or rogue search engines that don't acknowledge the Robots Exclusion Standard could disobey the instructions of your robots.txt. Finally, a curious user could examine the directories or subdirectories in your robots.txt file and guess the URL of the content that you don't want seen.
Webmasters and content providers began optimizing websites for search engines in the mid-1990s, as the first search engines were cataloging the early Web. Initially, all webmasters only needed to submit the address of a page, or URL, to the various engines which would send a "spider" to "crawl" that page, extract links to other pages from it, and return information found on the page to be indexed.[5] The process involves a search engine spider downloading a page and storing it on the search engine's own server. A second program, known as an indexer, extracts information about the page, such as the words it contains, where they are located, and any weight for specific words, as well as all links the page contains. All of this information is then placed into a scheduler for crawling at a later date.
QUOTE: “Ultimately, you just want to have a really great site people love. I know it sounds like a cliché, but almost [all of] what we are looking for is surely what users are looking for. A site with content that users love – let’s say they interact with content in some way – that will help you in ranking in general, not with Panda. Pruning is not a good idea because with Panda, I don’t think it will ever help mainly because you are very likely to get Panda penalized – Pandalized – because of low-quality content…content that’s actually ranking shouldn’t perhaps rank that well. Let’s say you figure out if you put 10,000 times the word “pony” on your page, you rank better for all queries. What Panda does is disregard the advantage you figure out, so you fall back where you started. I don’t think you are removing content from the site with potential to rank – you have the potential to go further down if you remove that content. I would spend resources on improving content, or, if you don’t have the means to save that content, just leave it there. Ultimately people want good sites. They don’t want empty pages and crappy content. Ultimately that’s your goal – it’s created for your users.” Gary Illyes, Google 2017
There are a lot of definitions of SEO (spelled Search engine optimisation in the UK, Australia and New Zealand, or search engine optimization in the United States and Canada) but organic SEO in 2019 is still mostly about getting free traffic from Google, the most popular search engine in the world (and almost the only game in town in the UK in 2019):

QUOTE: “So sites that don’t have much content “above-the-fold” can be affected by this change. If you click on a website and the part of the website you see first either doesn’t have a lot of visible content above-the-fold or dedicates a large fraction of the site’s initial screen real estate to ads, that’s not a very good user experience.” Google 2012

If you are just starting out, don’t think you can fool Google about everything all the time. Google has VERY probably seen your tactics before. So, it’s best to keep your plan simple. GET RELEVANT. GET REPUTABLE. Aim for a healthy, satisfying visitor experience. If you are just starting out – you may as well learn how to do it within Google’s Webmaster Guidelines first. Make a decision, early, if you are going to follow Google’s guidelines, or not, and stick to it. Don’t be caught in the middle with an important project. Do not always follow the herd.

Ever heard of Maslow's hierarchy of needs? It's a theory of psychology that prioritizes the most fundamental human needs (like air, water, and physical safety) over more advanced needs (like esteem and social belonging). The theory is that you can't achieve the needs at the top without ensuring the more fundamental needs are met first. Love doesn't matter if you don't have food.