This is as much about mind-set as outcomes as it will define your long term business objectives. It is relatively easy to have huge profit margins when trading on your own.
Apps are good
I am sure you will agree that a contracting / self-employed model for staffing would be the best way forward. This may cost the business slightly more short term but reduces employer liabilities and costs with everything from pensions to HR support. It also facilitates dynamic scalability.
The OP + 1 or 2 other business partners / investors as directors of the company, small office £10K-£30k per annum, then the rest done through contracting staff @ £30K-£60k per annum each. Notable other start-up costs, although these could vary hugely, may be IT and communication infrastructure and software licencing @ £10k - £15K, employers liability insurance, professional indemnity insurance (guessing £1m-£15m for undertaking sizeable contracts) @ £1K-£2K plus a couple of K again for misc. accountancy and admin fees.
thanks Scrutinize - these sorts of ballpark figures are v useful
I already have a good Firm of accountants and Solicitors, so that's one less thing to worry about...
one a separate note, what's your view on hiring friends or family - I know some capable people, but I've never worked with them, and more to the point I've never been their boss - lol