Nigel is right, though I did not get if there any website. If yes you need to set redirects, if no - just keep .org for your needs.

Redirects do not affect ranking, only in case when they are used in a wrong way. 301 is more preferable.

on-page,

technical,

off-page

On-page is basics and should be done first. You can see its effect just in a few months or weeks sometimes. When it is done properly, websites start ranking (of course with low competition keywords, but still it is the you're doing it right).

What is great here is that you can improve on-page SEO occasionally and detect what brings the best ranking results.

Technical issues are important too as indexing, mobile friendliness affect SERP in a positive way and actually they are important ranking factors.

Off page SEO is being discussed much though backlinks still work. There are good services for backlinks purchase just choose the best one matching your needs.

Hope that helped a bit. Good luck!

This is a weird situation, though in my opinion the damage is minimal as the main thing is that the page is seen by search engines.

Well I've been using linksmanagement for 2+ years and all my websites are performing great.

My niches are marketing, home improvement and education.

Of course there are websites of different quality, but I always check backlink before purchase to see how it is wrapped up with content so there are no links that look like a LQ spam. What I like about the platform is that new web pages appear regularly and I can continue buying links for my clients.

"I currently have a 301 setup for my http to https page" - great! Also, you should check if your inner pages redirecting from HTTP-versions to HTTPS too.

index.html should redirect to the homepage main version with 301 Permanent Redirect.

You should contact SEOs and get as much info about backlinks criteria as you can and then you have 2 options: outreach by yourself or hire the SEO specialist that you can trust. Here are some tools for outreach that can help:

https://moz.com/blog/14-easy-ways-to-find-any-email-address-in-10-minutes-or-less

And there is not fixing price for a link building per time. Backlinks differ in metrics and the price depends on the relevancy (niche) and quality of a website (outbound links, content, permanent links or not etc). Compare prices from different sellers and make up your decision.

Redirects do not affect ranking, only in case when they are used in a wrong way. 301 is more preferable.

"I currently have a 301 setup for my http to https page" - great! Also, you should check if your inner pages redirecting from HTTP-versions to HTTPS too.

index.html should redirect to the homepage main version with 301 Permanent Redirect.

on-page,

technical,

off-page

On-page is basics and should be done first. You can see its effect just in a few months or weeks sometimes. When it is done properly, websites start ranking (of course with low competition keywords, but still it is the you're doing it right).

What is great here is that you can improve on-page SEO occasionally and detect what brings the best ranking results.

Technical issues are important too as indexing, mobile friendliness affect SERP in a positive way and actually they are important ranking factors.

Off page SEO is being discussed much though backlinks still work. There are good services for backlinks purchase just choose the best one matching your needs.

Hope that helped a bit. Good luck!