Hi,
The answer to your question is dependent of a lot of factors like number of user, peak load, and usage pattern.
Here is a link to the system requirements:
docs.microsoft.com/.../system-requirement-business-central
In my experience RAM is more important than CPU. But i don't think i would go for less than 4 cores.
And in large implementations you need to monitor your servers.
I would also say that scaling out is better that scaling up. So have your BC servers in a load balancing cluster instead of trying to build one server that takes all your load.
And separate your DB server from your BC service tier servers.
