Hi
With respect if you wish to become self employed you have to do things for yourself. I will attempt to answer your questions here,but you will then have to start doing your own research which means trying to access the IR website.
You probably won`t be paying income tax at all based on you currently having 1 pupil. You will need to pay Nat Ins class 2 contributions...don`t entertain voluntary contributions.
I`m a bit hazy on the IR rules for second incomes as my teaching is my sole income.But there is a section dealing with this issue on the IR website. However I know you might be entitled to Working Tax Credit even if you are a single person if your income is below a certain amount.
It`s worth your while going into your nearest IR office and discussing your concerns with them.Be totally up front with them.I have found them very approachable.I would also book an appointment to discuss your questions with an accountant.Alternatively do a google search on accountants as I don`t know where you are in the UK. I also fill in the self assessment form myself and then go in and ask them to check it`s correct.You can save on accountants fees and your own time doing this.Accountant fees are tax deductible.
This link will also take you to the home page too
https://www.taxcredits.inlandrevenue.gov.uk....uk/HomeIR.aspxI remember there is another thread with some more info on this somewhere on here.Try a search or scroll back through the pages.It was pretty recent too.