Are all mirror-less cameras the same? Are the systems really identical - like peas in a pod? Can you buy one camera and use other lenses? Should you get a body here and the accessories there? How many forums should you read at any one time before your brain explodes?
To give you a quick series of answers; no, no, yes, no, none.
There are at least 6 mirror-less systems that I can think of and only two of them share similar lens mounts. With a bit of a fiddle and two trombones you can adapt some of the other maker's lenses to some of the other maker's bodies but you always drop some of the maker's automatic features...and you frequently pick up optical distortions that make the whole thing an exercise in futility.
While I love to hook up unlikely combinations of optics and sensors - after all I work in a camera shop - I have come to the conclusion that in general you really should stick to the lenses on offer from the particular manufacturer of bodies you have chosen. The exception to this rule would be if Zeiss offers a lens for your chosen lens mount. These are likely to be very good lenses indeed and you will be asked to trade many potatoes for them.
All the above leads to the subject of this post: the new Fujinon 10-20 lens for their X-mount cameras. Fujifilm are forging ahead with the APS-C sensor cameras - the new X-T1 being hot at present - and they needed to supply a wide angle zoom for the landscapers and interior shooters. The 10-24 will give the same angle of view as a 15-36 would on a full-frame camera, but with a fast autofocus or focus peaking on suitable bodies.
Note: The focus peaking really does work well for manual focus in a studio situation - it makes it easy to see in dim conditions when you are dead on for focus. It also costs a few potatoes but is well worth it.
