Local Deployment or Just Call the API?

A startup is deciding whether to self-host an open-weight model or call a closed-model API for a new feature. Current expectations: low and unpredictable traffic for the first several months, no data residency or privacy requirement, and a small engineering team with no existing GPU-operations experience. A team member argues for self-hosting anyway, citing "it'll be cheaper once we scale and we should build the muscle now."

1. Using this subject's decision framework, would you self-host or call the API given the stated conditions? Justify explicitly.
2. What specific condition, if it changed, would flip your recommendation?
3. Is "we should build the muscle now" ever a legitimate reason to self-host ahead of when the raw economics favor it? Give an honest answer, including the real cost of doing so.