Debt recovery.
How do your intended customers pay you? Will you need to invoice them? What will your payment terms be?
Human Resources/Employment Law: If you are employing anyone, don't fall foul of employment law. There are many providers of HR and employment law advice, I think from memory Natwest offer this service (MENTOR?) if you bank with them. The deal is that if you follow their advice
to the letter you are covered against any claims employees make. Even the smallest procedural error can cost you in a big way........ I know this from personal experience.
Employees: Don't promise them the moon and the stars to get them on board; the switched on people you want will see through bullshit. Be realistic; it is better for a job to exceed expectations than not deliver on promises. Your employees will never have the same emotional investment in your business as you, but people with families to feed and mortgages to pay will have a real interest in making your venture successful. A younger, carefree and more 'dynamic' employee may seem like a more appealing prospect but is more likely to disappear if the job doesn't deliver instant result, especially if his only fixed outgoings are giving his mum £50 a week and buying a bit of weed at the weekend
Good luck in your new venture. Will your customer base be the UK?
It will be more difficult, time consuming and stressful than you think. There will be things that you have overlooked, and change that you can't foresee that could adversely affect your turnover/profitablility (legislation/tech change/BREXIT/Carney/Cybercrime.......)
Have you run a business before? (I have) The sense of pride and freedom that comes from being your own boss goes hand in hand with what can feel like crushing personal responsibility when Mr Ratshit comes to dinner.
But with a fair wind, it will be worth it.