How to organize comments on the site for free?

Question

Search Engine Optimization

Good afternoon.
Given: a small WP site that should be able to comment.
Option 1 - open default comments for guests. There is a suspicion that all the bots of the world will become angry in an instant and in 10 minutes the unfortunate site will offer everything from lubricant to watermelons at 6 rubles per kilo.
Option 2 - default comments for registered users. Big hemorrhoids from the developer's point of view + when leaving registration by email again bots + hemorrhoids for the user (separate registration-authorization chain)
The advantages of options 1 and 2 will be that the comments will be on the site itself and the search engines will read them ...
Option 3 - put a social network widget. Ideal from the point of view of the user (no authorization) and the developer. But here's the problem, the site's audience is spread across OK, VK and FB ... Put 3 widgets each? ugh. Plus, from an SEO point of view, how do search engines deal with such comments today, evaluate positively the activity in them?
Option 4 - saas widget or wp plugin. There are many of them and most are either heavy or expensive. The issue of SEO is also relevant. But in general, the option so far looks the most interesting.
Summarizing the Questions
1) How SEO relevant is it to worry about comments at all? how vulnerable are options 3 and 4 in this section?
2) If you choose option 4, advise the service / openSource / plugin corresponding to the Wishlist (authorization through 3 designated social networks (or at least 2 without OK), simple authorization, minimal administration (deleting comments, banning objectionable, free or within $ 5 per month)
Thanks

Answer 1

Use the AnyComment + Akismet plugin.

Answer 2

akismet from the default WP installation does a very good job of dealing with spam

Answer 3

I like how DISQUS handles these tasks .

Answer 4

https://ru.wordpress.org/plugins/anycomment/
Used many comment plugins, this one is the best.
I advise you to watch / try.

Answer 5

Don't suffer bullshit. Download negative keywords on the Internet and write them in the admin panel. No plugin needed.