Advice?
When you are an employee you have one boss.
When you are self-employed EVERYONE is your boss!!
Speak to an accountant is first step.
He/she will give you info on what options you have with setting up a limited company or not, VAT implications or not.
Books as mentioned nowadays is dead simple with the correct accountancy software. (Follow accountants advice as their job is much easier if you use the same software they use and hence lower accountancy fees.

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You may need Public Liability insurance depending what you are doing and where you are doing it. (give me a shout if that is something you need to look at)
Advertising? How are you going to let people know who and where you are?
Don't get carried away and spend a fortune on Yellow pages etc. Dead easy to spend thousands and get virtually no return.
What works in cities is of little use in rural areas in my experience.
Skye (like most of North Scotland) is still a small place and word of mouth and recommendation is how the vast bulk of advertising is done.
A tenner for an ad in the local paper will bring far more returns than a grand in yellow pages!
I've tried every media apart from telly and largely it is a huge waste of money!
Don't listen to the salesfolk from Thomson etc about how many folk read these ads.
Use your own local knowledge and think if you were looking for someone to do something on Skye how would you find them?
Making sure you have enough potential work to get you going is the major hurdle, after that everything falls into place.
But as I said at the start be prepared to work a lot harder and longer hours than you do at the moment and your free time will diminish rapidly!
Folk say "working for yourself must be great?".
It has advantages but it is NOT nearly as easy as being an employee.