How to correctly configure a dedicated server to host several websites on it?

Question

Network administration

The first thing you need to know (this is also the reason why I ask such questions):

• I have absolutely no system administration and/or dedicated server experience.
  

The most I did:

• a trifle on the VPS, available only by IP address (for example, to demonstrate the work of a certain functionality)
  
• rental of standard hosting with PHP/MySql
  
• running Apache on your own PC
  

What I'm planning:

• Main: Node.js + ElasticSearch + MongoDB
  
• Standard WordPress site
  
• BackEnd for some mobile apps
  
• More may be added over time.
  

Why Dedicated Server:

• VPS prices are too high, at least for ElasticSearch (assuming to work with a lot of data)
  
• It can host more than 1 project. 1 main, the rest are secondary, not requiring a large number of resources
  

The main question:
How to separate this zoo from each other and should it be done?
Yes, I can just put all this on one big server with each other, but it seems to me (including for security reasons) that this is far from the most correct way. Ideally, I would like to have something like a centralized ISPmanager, if possible of course.
Side questions, which, in principle, can not be answered. I think there is a lot of information on these issues on the Internet:

1. How to monitor server health?
   
2. How to secure the server?
   
3. Basic tips for the absolute beginner.
   

Answer 1

The answer to the question is already in the question: ISPmanager may not take care of health (if you mean iron problems), but it will provide minimal security (there are built-in tools for this). For a beginner, that's it.