Can anyone explain the legal / tax side of employing freelance sales staff on a commission basis who will be cold calling business and residential customers?

I am negotiating a contract to supply customers for a company that will involve the recruitment of large numbers of freelance sales staff by me. I want them to be working freelance and not as an employee of my company so they will be registered as self-employed.

What would be the admin requirements for paying commission? Will they invoice me for offerring a service or would I issue them with a pay slip / receipt for services with no tax deducted, NI or tax code included?

Will VAT be paid on my profit after payment per sale to the agent or on the gross amount paid e.g. if I'm paid £50 per customer and £40 of that goes to the agent, would I pay VAT on the £10 or on the £50?

thanks