In the US you can start an LLC "a" and later on a Holding LLC "b" and make "b" the owner of "a", so that "b" is the parent (and holding company) of "a". It's really just about how ownership is structured, and it can be done later on.

You can also do it later on.

If you are the sole owner, then you can also do all of that in one business. I have my operational side and investments (like stocks) in the same company.

My plan is, to spin operational businesses off as soon as the legal risk gets too high or as soon as I seek for other 3rd party investors.