I think you're wasting neurons worrying about these things. Each person's ideal environment will change several times in their journey. If I haven't changed, then I'd still be using FrontPage 97 and HotDog today (BTW, Hotdog was the shizzle king back in the day!)
What's "right" for one person may not be "right" for another. Pick the tools you're comfortable, and enjoy using. And nothing is set in stone, you can always change/swap/replace/upgrade later a few years down the road as your needs and preferences changes.
A few direct comments on the topics you've raised (subjective: my preferences)
- OS -- who says you can only use one? Truth is some tools are only available on Windows, and some tools are only available on OSX. Ubuntu?.... I just use it for it's browser to test completed sites/projects.
Text Editors -- FREE is good in my book. And there's plenty of FREE options to choose from. Within the last 3 months though, I've settled/migrated to Visual Studio Code on OSX. On the Windows side, I'm using Visual Studio 2017. If you asked me just last year, I'm a Sublime/Brackets (OSX) and VS 2015 (Win) guy. I don't have any loyalty.
Web Browsers -- I test my client's projects on all of them. Plus, I also test them on iPhone, iPad, Win8 tablet, Android phone & tablets, Nook, Kindle devices. During development, Chrome is my default though. Have 32GB RAM, you'll have plenty enough for everything.... even simultaneous running virtual OS. (The screenshot above uses 4GB, with Windows, Ubuntu running, Email, 2 Chrome browsers, Sourcetree, Photoshop running... I still have 28GB free left).
Terminal -- most editors have integrated terminal within them (like VS Code). Any which Terminal program you use, you end up on the same place anyway. I just use my terminal for npm installs and brew update/upgrade... and running dotnet commands (new, build, run). Most of the time, I stay on the GUI land.