Street (landscape, sports, portrait etc.) photography should to be done (this) one way.
Do what ever works for you. Look to your mentors for ideas and tips, but never limit yourself just because someone else says there is "only one true way". Most photography evolves from the limitations of equipment, social constraints and fashions, but new rules are made by those who power on regardless of convention and learn to reinvent. If you spend more time trying to do as do or others say, you are not being true to yourself and will never grow.
Mirrorless beats SLR's or SLR's beat mirrorless.
Nope, they are similar but different. SLR cameras are still generally better at tracking focus (for now) and their view finders are clear glass, which some prefer. Mirrorless on the other hand can be quicker, smarter and lighter and can be reinvented to get around some technical limitations (face detection, video and electronic shutters etc.). SLR's have the two biggest names in photography behind them and the tradition and history that entails. Mirrorless are more innovative and interesting, but can be a bit thin in options. Time will only blur the differences more until it matters not at all what you choose, and that time is close.
You need full frame to be a professional.
This one is just crap. Lets look at it logically. The cheapest SLR on the marked today takes a better image than the best pro camera of 5-6 years ago. Each generation of cameras adds more of everything, but few in the industry want to ask, or answer the question "how much is enough?" as this will stunt sales. If you go back to the release of the D3X Nikon a few years ago, people paid $10,000+ for a full frame 24mp camera that did not even have a sensor cleaner! The current base model D3300 can match that camera for pixels, come close in low light performance, cleans it's own sensor and shoots video. Don't even get me started on print requirements! Ok, so while we are here. In a recent test a photographer showed two large (A1?) prints to a number of passers by (remember 95% of the people looking at your work are not photographers, but "passersby"). One was printed at 72 dpi and the other at 300 dpi. (industry standards suggest that if you do not print at 240 dpi+ you will not get gallery quality images). Nobody, not even an actual teacher of photography picked the difference between the two images. Luminous Landscape has a revealing article comparing the 50mp 5DS to the old 8mp 1DS in direct print comparisons, they are not as different as you might think. Ming Thein tried on the other hand to produce a print that held more detail than the human eye could see without assistance. He hired an industrial scale printer to do multiple, micro fine passes over the carefully selected paper to max out the resolution of a D800. He could only manage 11x14" paper before the test ran out of steam. The prints sold for many $100's to cover costs and in his words the whole exercise was pretty pointless, but revealing. Finally Pekka Podka has an interesting article on his blog comparing the OMD to the D800. So, to create gallery quality images at a reasonable size, you need...... a crop sensor camera of about 10-12 mp. We know this because people used to do it and still do.
What makes a pro photographer is actually pretty simple, know your process and HAVE A BACKUP!
More pixels make a better camera.
As above, the evidence says otherwise. Sharpness, light and composition are not controlled by pixels. More pixels technically make a bigger file and that should allow a bigger print, but that is only if the above considerations are met. Colour depth and "lushness" can be improved with more pixels, but so can detail smearing and image "noise". For more resolution to be achieved better technique and lenses are required and remember, resolution is not the same as perceived sharpness.
When a mobile phone has more pixels packed onto its tiny sensor, the pixels get smaller, gather less light, resolve less real detail and produce more noise through pixel failure, but still produce bigger files! The most important feature of a camera is the size of the sensor as this determines the size and density of the pixels and their effectiveness.
There is a reason that full frame sensors are just hitting the 40+ mp mark when phones have been offering this for a while. That reason is marketing. The marketing people control the sales of phones and small digicams and have two weapons; zoom ratio and pixels. These are easy numbers to identify with and the industry has trained us all well to respond to them. Better cameras are controlled by marketing also, but photographers know that balance is far more important, so the marketing/camera design appeals to other needs.
For a serious photographer there is no point in having a small sensor/high pixel/long zoom camera if the thing becomes useless in poor lighting and does not produce the images it promises. Most top of the line pro cameras are full frame with less than 20mp (the flagship 20mp D5 Nikon has just been announced). This is because if you want the very best performance in all other important areas (low light noise/grain control, processing speed, accuracy, image quality), the number of pixels still have to be controlled. So if you put pixels first, what is being compromised?
You need to cover "all the bases".
In the "5 stages of the photographer" the third stage (?) is collecting all the gear you can carry. No one is good at everything. Work out what you are interested in, get good at it and produce work. This will save you a lot of time, money and frustration. I know this because I have been down this road many a time. What you actually need is usually not much, what you think you need is probably more. I carried a macro lens around in my kit bag(s) for years. Switch brand or format, better get that macro. Turns out I hardly ever used them, so "just in case" did not ever really happen. My father in law on the other hand would use a macro or similar more often than not (the man actually likes spiders). Any reasonable close focus lens would do enough for me. I learned that one 6 lenses too late (bit slow, but I get there). By the same token, don't cut out lenses just to go with convention. Many landscapers use longer lenses and sports shooters find a use for wide angles and some dog photographers even use a fish eye lens. If you look in camera bag of most experienced photographers you will usually find only a couple of favourite lenses in preferred focal lengths, often specialist lenses and primes not zooms. They have worked out over time what works for them and that's all they carry. Try a day out with just one non zoom lens, surprise yourself.
Maybe this one is true;
No method, camera brand, opinion, technique or personal vision is better than another unless it pertains to you and your needs only. Be your own mentor, make your own rules.