I wasn't sure if I should reply here or start a new topic but I was searching on here for the very same questions. How much can I expect to earn?
One thing I did notice is people were being so honest with their declaration of earnings in terms of TAX/NI etc and going over threasholds and having to pay out huge amounts of money.
10 years ago I ran my own retail business (I also used to be a private hire driver), it was tough, but there are things I came to realise when it came to money. If money is paid to you through cash in your hand then techincally it doesn't need to exist, if however you purchased supplies with an invoice and that purchase belonged to a service you provided for payment then of course you need to declare where the money went for the goods you purchased. In essence there was a digital trail that you had to back up when it came to declaring things.
Unless we get clients who pay us with thier Barclay Gold cards or their debit cards, and as long as we don't physically bank our money then there isn't any physical digital trail to follow. No card transactions, no deposits in the bank. With this in mind, and of course for showing that you're activly working and paying your way. If you set a limit of say ?1500 pcm for your earnings, this is what you declare, anything outside of this you bank away privately. You would be earning enough to buy yourself a locked safe which you could store under the stairs or something where you live. It's secure and no one needs to know about it. As long as you're not splashing out on things all the time and making it plainly obvious that you've got more cash than you're declaring then you should be ok, secrecy is key though.