Need advice: Quit my job, currently on Engineer/Humanities visa, planning to switch to Student visa

Hey everyone,
I quit my job on October 20th and submitted the 契約終了届 (keiyaku shūryō todoke) to Immigration this week. I’m currently on a 技術・人文知識・国際業務 (Engineer/Humanities/International Services) visa, but now I’m planning to apply to a 専門学校 (senmon gakko) and switch to a Student visa soon.

Here’s the problem:
Since I’m technically unemployed and still under my current visa, I can’t legally do any part-time work, so right now I have no income until the visa change goes through.

Has anyone here gone through a similar situation?

How long did Immigration take to process your visa change?

Is there any way to legally work part-time during the transition?

Any tips on surviving this “no income” gap until the new visa is approved?

Appreciate any advice or experience you guys can share 🙏

by kotetsu3819