1. What is the minimum income in $USD for me to file taxes (as a 16 year old)? $400 of self employed income- it's the same regardless of your age.
2. Would the taxes be under my mothers name (my guardian) or mine? yours - you would file using your social security number. Nothing you earn goes on your mother's tax return - it is simply how it works.
3. Do I have to file "X" amount of 1099 forms for each client/job or can I just file one 1099 in a quarter including all of my gross income? your client should be giving you a 1099-NEC; if they don't you still have to report the income
4. Does the client I'm working for send me a form or do I manually have to get that myself? see #3
5. Would "under the table" pay like paypal or venmo be liable on my 1099? yes - there is no such thing as "under the table" - you are required to report all income earned - even if it is cash payments
6. Does me claiming myself as "self-employed" or having a "small-business" affect my mother's taxes or chances of me getting a student loan in the future for college? won't affect your mother's taxes, but FAFSA is going to ask about her income AND YOUR INCOME, so your income is part of the scholarship process. Hard to say whether it affects your changes of getting a student loan - are you going to earn $1000 each year or $100,000 each year?
7. Would I need to fill out the quarterly forms or the quarterly forms + the annual one? the tax return and the 1099-NECs you receive are completed annually. However, if you make enough money, then you might have to pay quarterly taxes, but that is just considered an estimated payment against what the annual form says determines you actually owe.
good luck being an entrepreneur at such a young age!
