How do I manage multiple domains from one droplet (to host all my landing pages for my different websites/businesses)

I have several businesses and some of them do not have a website, but we need to build landing pages for the different offer we’re running.

I want to create several different landing pages for each of our different domains. But I don’t want to create a droplet for each domain and then manage each on separately. I want to be able to quickly create landing pages, on the fly, for one domain and be able to do the same for another domain, without having to run a handful of different web servers.

Here’s an illustration of what I would like

Would Wordpress Multi-site be the way to go? What is the best resource out there to walk through the process and all the considerations you must take into account, when doing WP multisite?

I currently create landing pages on our Agile CRM but the problem with their landing pages is that they aren’t SECURE (no https) so it could flag users to not trust us when they land on our page.

This question went unanswered but was similar.

What’s the BEST PRACTICE here?

Basically I want to do what LeadPages and other “Landing Page Builders” offer, but not have to pay for their services, and run/manage my landing pages on my own.