As the series 2 SV6 being "Flexi Fuel"- E85, E10, 95 and 98, with the tune will I need to keep to one type? Or will I still be able to use any of those fuels?

If we tune for the least performing fuel then you would be able to comfortably use any higher performing fuel. For arguments sake, if we were to tune your car using 95 octane fuel, then you would be able to comfortably use all of the fuels you've mentioned with the tune we provide.