looking for a flat or spacious studio for rent in Berlin

I'm an audio software developer and a music scholar (PhD).             

For work reasons, I am looking to move to this city as soon as possible (current estimate is 15/23 June, but I have flexibility. I could also sublet a place before the dates above. I have a stable monthly salary, both from my work and a PhD scholarship, and have lived in Berlin for several years in the past and part of my family lives here as well.                

I am looking for a flat for rent in Berlin or spacious studio of between 30 and 60m2 and a rent below 900EUR (kalt). I am interested in arranging visits to any flats that fit these requirements and are available for long-term rental. I’m interested in the following areas (in order): Neukolln, Kreuzkolln, Kreuzberg, Schoeneberg, Friedrischain, Mitte, Prenzlauer Berg. I’m also open to a WG with like-minded people.