Yes, GPT-4 Turbo already exists and was released before GPT-4o. Turbo is a faster, cheaper, and more optimised version of GPT-4, designed to provide improved performance while retaining the same underlying model architecture.
GPT-4o (omni) is a more advanced release with enhanced capabilities across text, image, and audio inputs and outputs. It offers even better reasoning, speed, and versatility compared to GPT-4 Turbo.
So, while Turbo came first, GPT-4o represents the next step forward! 
They have a public market place already…
You’re correct; OpenAI has launched the GPT Store, a public platform where users can create, share, and explore custom GPTs.
While the GPT Store facilitates the distribution of these custom AI models, the monetization aspect is currently limited.
OpenAI is conducting a pilot program with a select group of builders to test earnings based on usage, aiming to foster a vibrant ecosystem where creators are rewarded for their contributions.
However, this monetization feature isn’t widely available to all developers at this time.