Sorry Rafael I missed this. I'm no expert, but happy to offer some advice. It's a very challenging format as it is so inclusive. Photography can be hard as its all about including the details you need and excluding all the clutter and stuff you don't, from this point of view painters have it easy.
You have 3 choices, Widelux, Noblex and Horizon. All have issues and problems unfortunately and my widelux has been fixed twice in 12 months due to banding issues. However for some reason it produces the best images, not necessary in sharpness, I can just compose with it better. The widelux and Horizon use aperture for focusing, some noblex models allow you zone focusing. You can look all the details up on google.
The trick, which I have not mastered - is to get close. Landscapes look distant and bland, busy crowds and built up areas are where these cameras seem to shine. I compose with my eyes, what you can see the camera can see, the viewfinder is a rough guide only. I hold it against my chest most of the time, all the indoor shots are a 1/15 second, which is a rotation of around 3-4 seconds. Hold you breath, look down at the camera, point it where you want the center of the composition to be, press the button, and stare at the bubble level, keeping it level. That's the best technique for 1/15 second shots. At 1/125 and above you can relax more and use the viewfinder if you wish. I shoot Tmax400 at 1600 and HP5 at 3200 to get the aperture into a zone where most things are in focus.
Get close, I can't say that enough, its very wide angle you have to be in people's faces to get decent shots. I am still working on this, only having ever shot street in this last 12 months, and living in the back of beyond gives me little opportunity!
The best images, have something going on in all areas of the frame - this can be difficult to achieve, although i do like some of my images that have a deliberately open area - some of them work, some of them don't. You need to waste a lot of film!
This guy in my humble opinion is the best exponent of the format, he is a genius.
http://www.lasthein.se/Email me through the site any time.
Dave