If the actors are sitting, you can hang a couple Kino's on the ceiling and soften them with diffusions to give a general exposure and then use another one for the face.
Do not bounce the lights off the roof of the bus because it's most likely another color other than white. You should bounce it off from a white card.
Definitely use gels to balance the color of your lights and those from outside. But keep the inside slightly warmer - more interesting.
No problem using Tungsten lights. Yes, they're more hot, use more juice, and you need to color gel them, but they can give you more kicks and more throw in distance. So if you need a wide shot, they might give you just enough power. And they're cheap too!
If you have more questions, you can also message me on Facebook: https://www.facebook.com/Solar.Productions
Good luck.
Eric