Hi.
I hold fellowship status with the International Association of Bookeepers and I have been a self employed bookkeeper now for 4 years.
You need to get accreditation from your governing body. ie, you need to be at least a MAAT to practice. You also need to hold a practicing certificate which also covers you for the Money Laundering Act 2006. Speak to the AAT and they can run through the procedures with you to gain compliance.
If you do not have the relevant qualifications to hold Membership Status but enough for Associate for example, you can still trade, but you need to get your Money Laundering Compliance through HMRC instead.
Also as part of your membership, you will need to gain a certain amount of Continuing Professional Development points per year. This can be achieved in may ways and again, the AAT guys can point you in the right direction.
Sole trader v Limited company. Limited company means limited liability but more complex to file accounts and you have to pay corporation tax and pay yourself though the PAYE system. Personally, I went for Sole Trader as Self Assessment forms are much easier to do every year. If my income takes me into the next tax bracket, I will rethink.
Yes to Insurance. Professional Indemnity protects you if you screw up. Particularly important if you are a sole trader and have any personal assets. Also Public Liability is definitely needed as you will be having clients to yours and you will be holding their books at your property.
I put business cards in the local cafes and builders yards and actually drummed up a fair few Self Assessments from that. I also gave my business cards to the local Business Bank Managers and have had positive responses from that also. Other than that, I have done no other advertising and I am incredibly fortunate to have enough clients to keep me going.
Also, you may want to consider looking at the courses that HMRC run (also counts towards your CPD) as they have very handy pointers when it comes to SA, VAT and Corporation Tax and the regulations surrounding these.
Can't think of much else at the mo, but will add if anything else springs to mind.
HTH
Feel free to PM me.