SEO For Site With 450 000 Posts?

Most of SEO methods I have done and seen always works with only few keywords - like 1-10 phrases, but how to do onsite optimization and offline link building with such huge numbers? I have this wordpress tube site I want to optimize but find it really hard to find any information on this kind of SEO. Does anyone here have experienced with this? Since there is no way this could be done manualy, I guess some SEO plugin might help, but I have no idea which one is good, since so far I usually work with much smaller amount of keywords I did most things by hand. Any suggestions on this topic are very welcome. Thanks for help guys.

70% link building to the home and 30% to internal links, your on-page seo has to be perfect this includes everything from keyword density, proper use of lsi, unique meta tags, images with internal links, every page should be have internal links to flow link juice try reading more about silo structure its complicated but if its well worth the time and effort.

Yoast normally works well, even with large numbers of posts. With that amount of content, I'm pretty sure you'll rank for a ton of longtail stuff by just formatting your Meta titles properly: https://yoast.com/wordpress/plugins/seo/
An alt tag plugin for images will help: https://wordpress.org/plugins/seo-image/
For interlinking content: https://wordpress.org/plugins/seo-automatic-links/

I am using Yoast SEO Plugin free version. Its Good. All in One SEO is also Good.

Normally do seo to homepage and categories only.

Thanks guys, now I at least know where to start.

I experienced the same thing. One that should be done is to rank keywords

Internal linking should be great from high priority sitesm ekse you will lose in Serps. link building is different in these campared to the olden days