PMJI : I have about 15 WP sites, aspiring to a few thousand more, mostly now in subdomains created for experimentation. It’s dirt-simple to create a subdomain, create a database, install WP, and get moving on something new. Any new idea can become a new site with its own personality/theme, plugins, and customizations.
Learn the pattern of getting through these basics and you can have a new site up in just a few minutes. I’ve found DH subdomain propagation only takes a few minutes from where I sit on the interwebs, so I go from idea to implementation as fast as I can click.
You can also host your custom work in the same site as WP, with .htaccess to route requests away from WP a you wish.
In addition to the Codex and thousands of blogs on WP tech details, there are a few Very good recent books on WP app development which cover internals as they discuss various concepts. This information is your fast-track to productivity.
That said, once you do get into this the details will keep you busy forever. You can get bogged down for days with nuances of plugins and themes, bugs, difficulties getting information, developers that lose interest in their freeware, and basic “why the heck isn’t this working?” But proficiency grows with time and the challenges just get more complex as you learn ask more complex questions.
Just remember “FOSS is only Free if your time is worthless”. You’re going to pay dearly for this freeware with your time. But I think the time=money price for this software is fair.