Short-term freelancing during unemployment questions?

Hope this is the right place, I believe the question about freelancing has been asked before but I need some help if anyone had done freelancing for a couple of months only…

I am leaving my full-time job end of this month and I have recently accepted a freelance job in Tokyo as IT developer. The position is 60 hours a month and will be earning less than 200k. My contract mentions I would be a Sole Proprietor and need to handle my own tax, insurance, etc… When leave my job I will be fully focused on job hunting, I also have another potential full-time job but it would only be starting by end of August. I hold the engineer/humanities Visa till 2026 and I am non US citizen if this info helps.

I am married and my partner is not working so she holds a dependent visa, I have a few questions if anyone can help:

1. As this freelance income for a couple of months until i land a full-time job, do i need to apply for certain things in Tokyo like a document for sole proprietor and Im not fully knowledgable but I keep seeing the words blue slip?
2. I am thinking to continue doing this freelance job when i secure a fulltime position as it does not take too much of my time, if so, it would be the same question to above
3. How can I calculate how much to deduct for all the taxations, insurances, etc… as I would need to issue an invoice to the company but when i receive the amount I am not sure how much to keep on the side.
4. Also as I have a dependent, does this mean I need to pay double on the deductions?
5. I know once I leave my job I need to inform immigration and my city office, but would I need to do anything else as I am doing this freelance job
6. If by the off chance anyone knows, not sure how to word this but would I still be considered employed if i do this freelance role that is less than 60 hours and therefore able to keep my Current work visa ?
7. Would also love any guidance and information if anyone has done this, as this would be the first ever I freelance and not working a fulltime job, have many worries.

Sorry if I ask a few more questions later on as Im still unsure on what to ask and the processes…..