Personally i did about 10 to get my technique right, i just practised on friends and family, i had fab training so was quick to start off. Really its personal preference as to how confident you feel
Its also personal preference how far you want to travel, i go all over, even if it means its not as "worth while" as someone who is closer, all tans are worth while in some respect as its word of mouth, just because your client lives a little further out, their work colleagues or college friends might not. The beauty of being mobile is you get to choose
Sit down and work out how far your willing to travel, if you need to add a mileage cost for people living further out and how much you feel you should be charging for a spray tan.
Its your business
HTH X