I have a weekly outgoings book and a monthly incoming book....it gets tedious being paid weekly and you know how much income you have if being paid monthly.If I was you adopt this.
You don't need a business account,just a current account. Keep all your receipts.
An accountant sorts my books out and I go into the tax office to have my self assessment form checked over.Very handy when you are stuck on a box. I then leave it with them and they do the rest.
National Insurance: Set up a DD for Group 2 and depending on how much you earn you may have to pay group 4.
Set aside enough dosh to pay income tax ( if any).Worth checking out the inland revenue website and you may be eligible for tax credits.
Bank statements et al,have to be kept for a minimum of 6 years.
I hate banks. If you are with a bank consider changing to Nationwide or even the Halifax,for example.
One more thing. It is pretty obvious,but being self employed it is even more important.
Write down your outgoings each month ie all DDs,Mortgage, Money for yourself,Petrol...literally everything...and budget for the lean months.
Good old pen and paper is the best for me and using online banking to check the depleting bank balance every day or so.
The IR are also very helpful,so it might be worth a trip into your local tax office to discuss things.And it's free advice.
Hope this helps.