Thanks for the input everyone.
I talked with a technician at fuji and he told me that I should stick with the 250D the whole way through. Like you said, if you do a good telecine and good keying it shouldn´t be any problems.
I´m shooting both exterior and in a big warehouse with daylight coming in. We are lighting the whole thing with large hmi:s. Then we thought we could use the warehouse as a studio and just put up the screen there, using the hmi:s as lighting for the actors. Saves time and money, he he he.
Would it be better to use a blue screen and light it with hmi:s? Or stick with the green screen?