Using Blue Tax Form as Seishain with Freelance Gigs

I'm currently working as a full-time WFH seishain at a company but will soon be getting extra income from freelance gigs (also fully WFH), so I'm looking into what I need to know in order to file my own taxes in 2025 for the fiscal year of 2024.

From my research, I have concluded that

1. I don't necessarily have to notify the tax office that I'm engaging in work as a kojin jigyo, but if I do, I have the advantage of being able to file with the blue tax form
2. I don't have to apply to be a qualified invoice issuer unless my freelance gigs suggest I do/show signs of not working with me anymore if I'm not registered as one
3. The white tax form is much easier to submit since it doesn't require any complex bookkeeping, but I can get more deductions if I file with the blue tax form

I'd really like to save as much money as possible through deductions, but I'd like to see if it's actually worth all the trouble of dealing with the blue tax form, or if I should just keep things simple and stick with the white form. Currently, I'm wondering the following:

1. Is it possible for me to use the blue tax form as a salaried company worker? And if yes,
2. Am I allowed to claim deductions on things like rent and utilities for both my salaried job and freelance gigs or only my side gigs?

Thanks so much in advance!