Go mirrorless if...
You want a small system, just like in the days of film.
You want very fast and accurate focus with no need to micro adjust.
You want real time WYSIWYG in the VF (say goodbye to chimping.)
Dust bunnies and view finder crap drive you nuts.
You want a very high keeper rate with few instances of blown highlights (no more DSLR chimping, use an in view histogram and get it right 99% of the time.)
You want to use old or new manual lenses (great manual focus aids.)
You want lenses that are (pretty/very) sharp wide open.
You want the ability to move your focus point to just about anywhere on the sensor.
You want an EVF to see in the dark with.
You want the best video.
The system offers something DSLR's don't...
Go DSLR if...
You like big fat cameras and lenses (seriously, some people seem to...)
You want the very best focus tracking (but I think it's probably ok to say that only the very best DSLR's do better than the very best mirrorless.)
You really must have an OVF.
You want to use a lens or gadget that will only work with your DSLR of choice.
The OP's needs...
Portraits, you could take with with just about any camera from MFT and up.
Kids and dogs, it depends how fast they are moving. You might be able to shoot them with a
second hand £50 CSC and a £30 lens or you may need £4,000 of DSLR kit.
Bands, I used to shoot a lot of bands with a Nikon 35mm SLR, ISO 1600 film and a standard f3.5-5.6 zoom lens. These days I think you could do it with just about any camera from MFT and up.
Street, I suppose it depends... some people prefer a smallish camera, a quiet shutter and a moderately wide lens set to zone focus and if that's the case you could do it with a very cheap CSC.
Well, that was fun

Good luck choosing
