Got a source for this one? 
I guess that Njalla, Porkbun and OrangeWebsite are indeed the 3 most common that I found after some research myself. 
And yes, companies might blacklist you if you use some “off the grid” registrar because of some shady people tainting a given registrar.[1]
Yes, buying from a big name will always open you all the doors.
Cloudflare is about Security but not Privacy. And it is probably one of the most well-known one, I wouldn’t be too surprised if it might be known even by non-techies[2] at this point given the few downtime issues with had because of them (bringing Signal down etc…).
As a whole, the lower you go from an infrastructure POV, the cheaper it is.
Hence, Heroku $$$$ > DigitalOcean $$$ > AWS $$ > own the hardware $.
But it will be less friendly to use, with a disgusting UX and a “figure it out yourself bro” kind of mindset.
You get what you pay for (convenience VS well-priced).
Getting into hosting stuff on the Cloud (like GCP, Azure, AWS) is its own skillset entirely with certifications etc. Wouldn’t recommend this one unless you want to have a career in that specific field.
Also, you could probably host all of this on a RaspberryPi at home, cheaper, more in control and you don’t really get a lot of benefits from having it hosted on a VPS directly.
Okay, maybe buy a x86 with an Intel N100 if you want a closer architecture to the one used by VPS providers but in the end…it’s still just Linux so 99% of it will be transferable from local machine to some random VPS. 
Overall, DigitalOcean is a solid run for your buck.
And yes, it will always be over-priced for what it is because you’re renting out from someone and they need to have margins. 
DHH talks about this quite well. Their scale is not yours but again, buying real hardware and leaving it in your closet will always be cheaper/more powerful. 
PG has a cluster spread over 3 locations apparently. Not sure what are the VPS tho.