A great number of my potential (and hopefully future) customers use WordPress and ALL of my beta customers use Wordpress. The field I'm in requires that my clients have some type of web presence, basically a 'brochure' website and of course that's a field WordPress seems to cover quite well.
My question is regarding writing a plugin for my customer's website that integrates with the services I offer. I have roughly 12 years of PHP experience (last touched 5.3 or so somewhere around 2009) and I know it's changed but coding it shouldn't be an issue for me. I do have questions:
What version of Wordpress should I aim for? 4.9 (which requires PHP 5.2...)
What version of PHP should I target? I know this relates directly to the question above, but 5.4.x is dead and no longer supported, right?
How hard is it for a customer to upgrade Wordpress versions? I seem to remember that upgrading Drupal 6.x websites was a nightmare and you'd better have your backup ready to go.
Is PHP 7.3 compatible with Wordpress 4.9?
Basically, if someone could do a greenfield Wordpress Plugin write up in 2019 I'd be thrilled.