I could built you so many different showers with that exact set up. For one you can use the existing drain location and switch out the old drain pan for a new clamping drain and custom shower pan or a linear drain and custom shower. Building a custom shower starts with taking everything out and starting new. New tile prep. New tile. New plumbing. New fixtures and on and on.
Your toughest task is setting up a budget for this new shower and finding out if you can afford to do the entire shower custom or work with some ready made shower kits. Find the number you are comfortable paying and then work backwards. Make sure you budget only 70% of your maximum so you have a little in the kitty for pop ups.
Loads of my clients hire me to build the shower pan, curb, install the backer boards and waterproof the shower - then they take it from there. If you can do it all you only need to budget for the materials.
If you only have one shower then building a new custom shower can be a real drag so faster methods and more expensive shower building materials can save you some time.