Portfolio of multiple small businesses

Curious if anyone here tried building a small, lean portfolio of businesses once their first one finally stabilized?

My experience has been that after getting one venture to a steady place, starting up another isn’t as chaotic as it used to feel especially as mine are either online or high-margin, low volume services. I’m doing it in a bootstrapped way, tiny team, a mix of contractors and part-timers, with maybe a couple full-timers coming soon.

What I’ve noticed is that the shared-services layer starts to make a big difference in sharing costs across different corporations. Accounting, marketing, some backend ops, general systems. Even if the businesses aren’t in the same industry, some overlap usually shows up, and it cuts down the lift on getting a new project moving. Some staff as well that are good at one skillset ops wise are able to pick up similar ops tasks even in a completely different industry.

I’m wondering if others here have taken the same approach. Not trying to build a giant portfolio or anything, just a few small, steady companies that benefit from each other instead of running everything as totally separate entities. Curious what your experience has been, especially around what worked and what didn’t.