I'd seriously consider subcontracting these people instead of employing them, so they give you an invoice and that's all you pay. Very common here. Otherwise you'll be into social security (employee and employer), maybe income tax for the higher earners, and laws on working hours, paid leave and paid public holidays which are draconian for the employer. Do you know, for example, that your staff will be entitled to double time on some holidays if they don't work, and triple if they do?
That said, you can find the relevant laws on the web, although they need a lot of interpretation. I'll post the URL if I can remember it.
Peter Jones FCA