With any small business, having been involved with them for more years than I care to recall, two things are of vital importance:
1) A shareholder or partnership agreement – right at the outset. It’s a pain, but will save untold angst further down the line.
2) Good accounting – it’s dead easy now (and cheap) with the likes of Kashflow or Xero
Find a good small business accountant to advise on the best treatment of personal and business tax.