1) Like Wordpress' Multi-Site, which allows the User to control and manage multiple domains (yes, different) under one admin system, is there such a thing for Node.js applications? Using Express/React/MongoDB. If not, how will this work?

2) When creating a Search Engine functionality (like google search), what are the most basic parameters to create one these from scratch? It's basically a query looping over your database and doing a "get" request to bring those results into an HTML format. Right? How do I make this even more complex and efficient (Time/Space complexity).

Hi, first what comes to my mind, have seen it mentioned recently, here in this book:
https://www.amazon.com/dp/1593275994
That is concerning your second question.
What about the first one, well, I'm curious myself now.
Both questions are actually interesting, I think.