First of all, congratulations on choosing solid components for your starter setup, and welcome to the hobby. Your statement “the best possible sound quality from my system” is a deeper rabbit hole than it appears. One that has trapped many of us for years, though we’re all happy addicts
My main recommendation is to focus on mastering your room and speakers first. There’s a learning curve, but it’s extremely rewarding. Since you already have a measurement mic and REW, you’re well equipped, learning how to measure your speakers with REW is fairly straightforward. From there, take the time to truly understand your speakers: their crossover behavior (phase shifts), bass roll-off characteristics, whether they prefer placement near walls or further out, optimal spacing between them, and their distance from side walls for best phantom imaging. I suggest selecting at least 20 high-quality, demanding stereo tracks that you use consistently to evaluate your system, and learning those tracks inside and out.
A subwoofer can be a great upgrade, but proper integration is an entirely different challenge that can take years to master, so I wouldn’t rush into it. For most music, your speakers when placed correctly should provide sufficient bass on their own. Start by addressing bass peaks early. In many cases, just two or three PEQ adjustments are enough, even using something like a WiiM. Be aware that our ears adapt quickly to what we hear regularly, and it’s easy to start thinking boomy bass sounds good (I’ve seen this happen with many analog-only vinyl enthusiast friends)
Most automated room correction systems will auto-degrade sound quality unless you spend serious time on manual tuning, and there’s no shortage of bad advice around them. Dirac ART is one of the very few that can currently surpass even the best manual results largely due to its true MIMO architecture (though that gap may not remain for long - PS that was a hint!). A1 is a close second (I might be biased!), but despite being free, will still require a Denon or Marantz AV receiver, a significant and, in my view, unnecessary cost for a stereo-only setup.