Thinking of installing multisite on a new site

I just installed my site new with wordpress less than an hr ago and thought I’d go with a multisite instead.

I plan on using wpmu plugins with Divi themes and plugins.

I am reading up on wpmu mutilsite article and came across this statement

If you’re converting your existing site to a Multisite network, you follow the same steps as above with one exception: you won’t be given the option to select subdomains or subdirectories. If your site has been in existence for more than a month, you’ll be forced to use subdomains.

Since it was not explained in details, how will this negatively impact my multisite? I assume I need this subdomains/subdirectories for my potential clients.

Also if this site grows I plan on moving to a different host and also found some of your articles on how to do that.

If I can get answers on these questions and anything else you can help me with before I convert my site it would be appreciated.