How do you split AI models across ideation, math, and coding?[D]

A recent graduate is managing 3-4 projects concurrently and relies heavily on a GPT subscription, specifically web ChatGPT and the Pro model (5x), for ideation, brainstorming, and formulation. They are also exploring GPT 6 Astra, Claude Opus 5.5, and Claude Fable 5.1, and are open to other AI model recommendations to support their workflow across different tasks.