Those aren't errors just notices and they're fine. Fingers crossed it will work for you 
There's no link sadly between module version and shop version, so a module won't ever check what version of PHP you're running before an install or update. Ideally a module developer should update the details of which versions it works with (factoring in PHP compatibility), but sadly that just doesn't seem to happen.....
PHP 5.6 is seriously old and hasn't been actively maintained for some time now. If you want to see how far behind PrestaShop 1.7 is with PHP then compare the system requirements link in my post above with the official PHP supported version list! There was no PHP 6 but even so, PHP 5 dropped off the list years ago.....
EDIT: 5.6 was unsupported as of 5 years 8 months ago......