What upgrade path for MySQL and Php should I take ?

[fuzioneer 1]

Got a very customized version of OsCommerce running and its running on some very old versions of Php/Mysql and Apache (

Apache Version	2.4.41
PHP Version	5.6.40
MySQL Version	5.6.45

I am creating a dev server to test what breaks when I upgrade different aspects so that I can fix the issues and upload changes before switching main site Apache/MySQL/PHP versions.

Is there any path which will cause the least issues and give me the most benefits in performance / security ?

i.e. Should I go for PHP 7 or 7.3 ?

With MySQL should I stick with it and upgrade to latest version or switch to MariaDB which seems to be the better option ?