Best to avoid girls who have drivers, can't trust what other "jobs" those drivers do.
Foreign girls who aren't comfortable and familiar with London may only take taxis, so it's up to you how much you want to spend on those as they will probably be extra to her fee. Always confirm with girl if she's covering her own travel expenses.
Girls who are au fait with taking public transport may be your better bet, and they're probably happier to travel further.
Girls usually state on their AW profiles how long they will travel for.
For your first outcall, if you haven't already decided not to, best not use your own place.