Janos:
In the first instance your accountancy fees will go up, and that will increase as the year goes by as they will have to do a regular pay roll for you too. So speak to him about his prospective charges. In the longer term you should benefit from paying less tax, which lets face it, is the main reason people do it.
As a sole trader you are taxed on all your income, but as a director you can take a small salary and then the balance of your wage as dividends, on which the tax rate is lower. So look at your turnover, profits and accountancy fees and make a decision. Extra kudos from trading as a limited company is minimal.
Fair comment regarding the accountancy fees, these leeches will ■■■■ your last drop if you don`t keep an eye on them 
I personally use a local lady to do my book keeping and wages, her monthly fee is very competitive and she is far cheaper within that fee doing the payroll, she also presents the “books” in a professional way which in theory keeps the leeches fees lower.
The leeches will try to bend you over, you just need to stand up to them…
Just use the leeches for end of year signing off ect…
It suits me, it might not suit everybody 