Below is my own professional history to give some context to my current skill set. I have been a front-end dev for 18 years. My tools of choice are:

HTML5
CSS 3
JavaScript
WordPress
PHP (but not my strongest skill as I don't write it too often)

I first of all would like to become a better and more 'full stack' developer, and I have a business idea that will hopefully allow me to move in this direction. The queries I have will result in which approach I take here. One of the most important aspects to me is the system being 'future proof'. If successful I know I will eventually bring additional developers on board, and they will likely be better developers than me! I want to avoid them having to rebuild the system and would like it to be something that they can just expand and improve on.

The business which I'd like to create is the following (in a nutshell), I have ideas for many more features, but this is how I'd like to begin:

Web-based system for gym management & marketing. Specifically a class-based gym

One-stop shop for a class-based gym owner
Sell memberships
Manage class bookings
Reporting
Automatically generated website
Choose a pre-designed template and amend the content through their dashboard
Marketing
Easily send a newsletter to members
Book a free trial form on the website linked directly to the booking system

Important requirements

One system, one dashboard. I would like the gym owner to have one place to control everything. Members, marketing, and website amendments.
Future proof. These features are the bare minimum and I'd like to keep expanding on the features as time goes on. Things like uploading programming for members, messaging between members and admin, and selling merchandise via the website.
Fast to load & secure. I live in the WordPress world right now, which isn't the fastest or most secure environment. I appreciate there are better ways to develop a system like this, but I'm a little clueless about where to start.
Mobile. The data created should easily communicate with a mobile app that customers will download to manage their memberships and class bookings.

TIA to anybody that can provide some guidance on where to start here.

A White

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