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

A recent graduate is managing 3-4 projects concurrently and relies heavily on AI models for various tasks. They find a GPT subscription essential, utilizing web ChatGPT and the Pro model 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 for their work.