If you don't mind me asking.....why ?
It seems a strange choice, given the fact permanent employment is preferable to the fabled circuit.
However, if you do decide to go down this route, there's only one real option for you in answer to your query.
Get a good, very good in fact, accountant.... and let he / she do all the work.
You will have to pay of course, but, the savings ( monetary, time and effort )are well worth the cost to yourself.
And good luck in your dealings with the social parasitic sewage called "recruitment consultants "........