Can a “normal” user see all processes with htop

The way I achieve this is what you suggested:

Make a secondary Admin account and then take away your admin privileges.

I'm almost certain that it is the only way to achieve this.

Do NOT remove your Apple system provided python version found at this path: /Library/Frameworks/Python.framework/Versions/2.7

In fact - you should never mess with any Frameworks under /Library/... unless you know what you are doing. Your OS may have tools that depend on this version of Python that it ships.

After installing brew - did you run

brew doctor

It should tell you if you have any issues.

Also - be sure your brew install python3 (note there is not a space - 'python 3')

After installing your new Python - brew should put it under /usr/local/ not /Library/...

I suggest you use either Homebrew or Macports - NOT both. Make sure you follow the directions on their webpages and set your PATH in your .bashrc or .bash_profile properly.

After you set your PATH in those files, don't forget to "source" the files - or simply close and reopen terminal to "refresh" your environment to the new settings.

Good Luck!