You'll be fine. The Mac doesn't use PHP for anything. You don't have to install PHP 7. That link I sent also includes 5.6 but it also includes all the extensions you need which the standard version does not.
Trust me, you'll be fine.
'brew' is a 'package manager' for the Mac. It allows you to install all manner of things that are not easily available for the mac in the manner of 'apt' and 'yum'. Once installed, you can just do 'brew install mariadb' and wait for it all to compile.
Having said all that... it's not quite as intuitive as using Linux. Certainly not for development. In the office I use a mac for day to day stuff and a separate Linux box for dev. At home I use a Mac for everything.