Change website, theme and primary domain with a one-domain hosting plan

Hi community,

I am planning to launch a brand new website on a new top level domain, but without changing the hosting plan with my provider (SiteGround). This plan allows me to have one top level domain. As far as I understand this can be achieved using a multisite setup. I figure there’ll be several steps to take, and with my limited (!) knowledge of WordPress I could use some proper guidance on how to proceed. So, you’re comments are more than welcome!

Should this topic be posted in the wrong forum, I’d kindly request the moderators to move it to the applicable one. Thanks in advance!

Here’s the objective:

• I have a primary domain, which is running my current WP.org website.
• I bought a second domain, which is to become my primary domain.
• SiteGround enables me to simply change the domain linked to my hosting account.
• Before switching domains I’d like to build and test my new website.
• A little downtime while switching is acceptable, but should be limited as much as possible.
• I’d like to keep my current (old) website as a sub-domain of my new primary domain.

Below are the steps I figured out so far, but I presume there are more ways that lead to Rome.

• Create a temporary sub-domain on my current primary domain.
• Instal a tool or use multisite domain mapping to enable multisite management.
• Instal a theme and plugins for the newly created sub-domain.
• Build and test the new website on the sub-domain, without having Google index it.
• Make a full back-up of both the old website and the new one on the sub-domain.
• Migrate the new website to the new domain.
• Check and restore all internal links, and publish the new website.
• Create a sub-domain on my new primary domain.
• Migrate the old website to the new sub-domain.

My questions:

• Are the above steps correct? Are they in the right order, and are any steps missing?
• Do you know of any source that describes in detail what to do?
• Do you have any advice in general? Is there a smarter or easier way to get the job done?
• If I should create a multisite first indeed, which is the easiest way to go for a novice? Using a plugin or follow the instructions at WPmudev.org?
• Could I use a plugin like Duplicator to migrate my new website from the old sub-domain to the new top level domain? SiteGround has its own tool as well, but that doesn’t seem to be suitable in this situation.
• Can I manage my old website, its subdomain and my new domain all from the same WP dashboard? I’ve seen posts about tools for either multisite OR multiple TLD management, but not for a combined situation. So is it possible and feasible, and if so, how do I achieve this?
• If not, should I create a new WP.org account and setup my new website there? In that case, can I build and test it there while it is not yet linked to a hosting account? Mind that I can only have one domain hosted at SiteGround.
• In case I need to create a new WP.org account, can I still use the paid plugins I have for my other account?

Many thanks in advance for your response!

Cheers,
Jochem