Does anyone have any experience with any of these and can give some tips? The only one that seems to be really in my price range is the Olympus I guess...
They're all good cameras perfectly capable of taking good photos. At this point in the game for you, I would suggest being sure that your choice of camera and lenses are flexible enough to allow you to explore the many different facets of photography to allow you to discover what areas you like the most. Then worry later about getting better gear that is specialized if you need it to allow shooting things you want to shoot that your current gear limits.
Also can anyone inform me as to the compatibility between different brands of mirrorless cameras and different lenses?
Any of the Micro Four-Thirds cameras from Olympus, Panasonic, and anyone that might make one can interchange with any other Micro Four-Thirds lenses and flashes. Other than that, everything is pretty much a proprietary system. If you go with Fuji or Samsung¹ you'll be limited to only lenses and other accessories made specifically for that system.
¹ Do note that Samsung pulled out of the interchangeable lens camera market almost two years ago, so the NX mount is effectively dead. If you decide to go with Samsung now, when it comes time to upgrade you'll almost certainly need to change systems.
The Canon M series cameras are fully compatible with all EOS flashes and, using an adapter, fully compatible with Canon EF and EF-S lenses as well as with EF-M lenses that don't require the adapter. With most other adapted lens scenarios you give up speed, functionality, or both. With EF/EF-S to EF-M you only give up the lens compactness factor.
Could it also be that a small SLR would suit my needs as they don't appear to weight much more than the mirrorless ones such as the canon EOS rebel sl1 or the sl2 could one of these be the pick of the litter?
- With a smaller DSLR you give up a bit of the compactness of most mirrorless cameras. For most lenses in the normal ranges (focal lengths about one half the sensor diagonal to about 1.5X the sensor diagonal) the lenses are also lighter and smaller for mirrorless cameras.
- With a smaller DSLR you gain a true optical viewfinder as opposed to an electronic viewfinder. For more on the differences and advantages/disadvantages of each, please see: Why are SLR mechanisms still prevalent among high-end digital cameras? and What are the technical advantages and disadvantages of mirrorless?
- With an SLR in the Canon or Nikon systems you gain a lot in terms of lens selection. No other system comes anywhere close to the wide variety of lenses available in the Canon EF and Nikon F mounts.
One thing to be aware of is that the size advantage for mirrorless gets less significant as one uses longer focal length lenses as well as very wide angle lenses with very large maximum apertures.
- A 15-40mm f/3.5-5 lens for µ4/3 will be smaller than an 18-55mm f/3.5-5.6 lens for APS-C which will be smaller than a 24-70mm f/4 or 24-105mm f/3.5-5.6 lens for FF.
- A 200mm f/2 lens for any of them will dwarf all three respective camera bodies.
- An 8mm f/4 wide angle for a µ4/3 that gives the same angle of view as a 16mm f/4 lens for FF (or an 11mm f/4 for APS-C) will be larger and probably more expensive for the same image quality.
That's one reason the lens selection for the EOS M systems looks more limited than it really is. Canon offers plenty of EF-M lenses where they can be made smaller/lighter than their EF-S/EF counterparts due to the shorter registration distance of the EF-M mount. On the other hand, for lenses where there's no real size/weight advantage to using the shorter EF-M mount, using the same electronic protocols for both systems allows adapting EF/EF-S lenses to an EF-M camera means nothing is lost with regard to metering, aperture control, autofocus, etc. Since the EF to EF-M adapters are only spacers that pass through full electronic communication between the camera and lens and don't have any optical elements in them, no image quality is sacrificed either.
I know that when posing these questions it is assumed that you have a more specific purpose as to what you want to shoot, but as we are starting out we don't have any specific aims, but for now I can say that I would be interested in photography as an art, shooting mainly streets, landscapes, nature, concerts (so good in low light would be good) people in their settings, people interacting with each other, and people with a blurry background, I have little interest for now in fashion photography shooting sports and wildlife.
For your intended budget all of the cameras you have listed are about equally capable of dealing with most of the things you have listed. As you shoot in lower light and want to use shallower depth of field (blurry backgrounds), sensor size becomes more of a factor and larger sensors, such as APS-C, will give you more of what you want than smaller sensors, such as µ4/3, will.
For the low light usage and blurry background portraits you'll probably want to include a fast prime lens (a wide aperture lens with a fixed focal length that does not zoom). Most camera systems typically have at least one budget fast prime. For DSLRs it is usually a 50mm or 35mm f/1.8. For µ4/3 it's something like a 25mm f/1.8 or 20mm f/1.7. But you also need to consider the "kit lens" that offers a wide focal length range even if it isn't as good in low light due to its narrower maximum aperture. This will allow you to explore different focal lengths/angles of view and how they affect your photographs.
Keep in mind that for some things, such as low light concerts, nothing in your budget range will shine as well as a much more expensive full frame camera and very fast lenses in the hands of a seasoned photographer. Theatrical/concert photography is about the most challenging there is, both in terms of pushing the equipment you use to the absolute edge of their capabilities and in terms of requiring every bit of skill and experience you might have as the photographer. It, along with shooting sports/action in low light, is where the differences in gear matter the most. Although it discusses an APS-C DSLR versus a FF DSLR, pretty much everything in this answer is also applicable to a comparison of smaller µ4/3 sensors (17.3x13 mm) to APS-C sensors (≈22.5x15 mm for Canon, ≈23.6x15.6 mm for everyone else).
We've got a pretty good collection of questions with the concert tag, so be sure to check them out. There also plenty of questions here about landscape, nature, portraits, and street photography. You can search for terms by just putting the words in the search box, or you can search for questions specifically [tagged] with that term by putting the term in brackets with dashes instead of spaces between [multiple-words].
Overall, a smaller system like the Micro Four-Thirds cameras and lenses and, to a lesser extent, the mirrorless APS-C cameras and their lenses trade a bit of image quality in exchange for compactness. Just how significant the difference in image quality and the difference in size/weight is varies from one photographer to the next.
For some types of photography there will be almost no noticeable difference.
For other types there will be considerable compromises in image quality to enjoy the more convenient form factor.
As I'm sure you have already noticed, mirrorless APS-C cameras such as the Fuji X series also tend to cost quite a bit more than the smallest entry level APS-C DSLRs. In return you usually get image quality and features/controls more comparable to higher end APS-C DSLRs that are priced more similarly to their mirrorless APS-C counterparts.