I never use social signals and i rank just fine without it, i have run several tests and there is no absolutely evidence at all that suggests that social media has any effect on rankings at all...
Also, I would not use niche-edits but, put that money into building my own PBN where the P (private) is very important, niche-edits are extremely overpriced for the results you get (same goes for guest posts) just a waste of money.
Also waiting to start with backlinking makes no sense, i never wait, when i build a new site i throw around 30/40 articles on it and when it is indexed (most of the time within a week or two) i start backlinking, no need to wait and no need to make it complicated with tiers of quality links.
I throw everything in the mix, do follow, no follow, some comments, PBN links and some charged up web 2.0 properties, cus that is how it also works in the real world with real sites that are not being built to manipulate rankings.
If you think you can outsmart Google with this easy to catch, riddled with footprints method... Then be my guest, but you are making it way more complicated than really needed.
Stop overthinking it, it isn't that complicated!