In order to find out approximately how many (and how powerful) PBN domains you are going to need in order to rank #1 for one of your terms, you'll have to roll up your sleeves and do some detective work on your top 5 competitors that are currently ranking for those particular keywords.
1. Do some research on the domain/page they are currently ranking with.
- Check the age of the domain
- Check the volume of unique referring domains to that domain or particular page
- Check the PR of the domain
- Check the page and domain authority.
If you don't have a website you want to rank with, go buy an aged pre-owned domain that is close to the one your nr 1 competitor is currently ranking with. So if the top ranking page is on a 10 years old, PR 4 domain with 100 referring domains, ideally, you want to get a similar site as your money site, as close to your niche as possible.
Go find and buy that domain.
2. Do some research on the links of the ranking site/page. You'll need an aHrefs/OSE/MajesticSeo license.
- Check the total number of unique referring domains (that's unique link per domain you'll want to simulate with your PBN).
- Check the metrics of each page hosting a link and export that information (DA/PA/TF/CF/PR).
- Check if those pages have any links themselves, write down the number (if they do, you might want to GSA your way to the natural links pointing to the PBN domains you're planning to buy...)
Now do this for all your top 5 competitors and analyze the data. This should give you an approximate idea of how many and how powerful PBN domains you are going to need in order to simulate what they are doing in order to OUTRANK them.
That should be it.
Of course, you can do this, or you can do it as I do it and simply get 50-100 PBN links from the very beginning towards the same quality aged PR domain and simply patiently wait for Google to index all those posts and track rankings meanwhile. Then slowly add more batches of PBN links if it's not enough.
So it's the quality vs quantity approach as always. The last one saves a bunch of time. But you really have to know what you're doing.
Alex