You might be interested in a dog sled photo workshop that gives you some very interesting views of sled dogs and techniques. Check out dogsledding.com. Look for their special trips and you will see a dog sled photo workshop led by photographer Lane Kennedy. I took the workshop some years ago and found it very interesting.

Forget the issue of a mirror. People who worry about such things are not photographers they are tech geeks. However, having shot with a 5dsr since it came out there is one thing you should consider. You need high quality lenses to take advantage of the 50MP sensor. I use all L lenses. I have owned some of them since I shot film. You will get great images with the 5ds. You may not have all of the bells and whistles of the new mirrorless cameras, but the only Canon you can buy that will mach the image quality is the R5 for $4000.00 I also shoot with a EOS R, and I like it, but for high quality landscapes I always pick up by 5dsr.

I have used Capture One since Apple abandoned Aperture. (Captureone.com) I really like it for organization and photo editing. It is a very good RAW editor and has built in profiles for most cameras and lenses. They publish many free training webinars and you can try it for free for thirty days. Good luck.

I had a Sony A6400 for a while before I sold it because I did not like it. It had a problem with the lens making a direct contact with the camera body. The lens would not work and I received the same error message you received. I sent it back to Sony under warranty and they repaired it. Try taking the lens off of the body and reconnecting it with a strong twist, otherwise I would send it to Sony for repair. Good luck.

I shoot raw and convert to black and white using Capture One Pro. When you say you may shoot color and then convert you may find hard to obtain quality black and whites if you are converting color jpgs. Raw images always start in color because they import all of the data. However, they give you all the data you need to produce high quality black and whit images. I am not familiar with the post processing software you are using, but most software has a method of producing black and white images from raw photos. You can reduce the saturation and produce an image that looks like black and white, but you are much better off using the black and white conversion that should come with your software. I would look for better software if your's does not permit conversion.

No - You can use everything he writes about with any flashes that can be used off the camera and synched.

I urge you to read "The Speedliter's Handbook" by Syl Arena before you leap into flash photography. It will tell you all you need to know about the subject.

I always reformat my cards after the images are downloaded to my computer and the computer has completed its daily automatic backup. That way I have at least two copies of the original image. That way I can reuse the cards. If I want to take the images somewhere I simply export them to a flash drive.

I have used a 5dsr since it came out. Saying it is not good in low light is not an accurate statement. The camera does not perform as well as some other cameras at very high ISO numbers, but this of us who rarely shoot above ISO 1000 have not problems. I generally do not want to shoot at very high iso because when I shoot a dark scene I want it to look like a dark scene. The attached image was taken on a tripod before sunrise at Iso 400. The camera handled this early morning scene without any problems.

The R5 is a better camera than your 6D. It has a 45 mg sensor compared to the 20mg on your 6D. This alone will give you much sharper images plus the ability to crop and maintain high quality images. The Person who said "For the R5, you gain both FPS and pixel resolution, but until you start buying RF lenses and selling the EF, you're not maximizing the money spent on the mirrorless body (either model)." is not correct. As long as your EF lenses are high quality "L" they will give you very good pictures. I have a large collection of these lenses and they work very well on my EOS R with the use of the Canon adapter. I think the RF lenses may take better advantage of the built in IS on the R, but I see that as a small advantage to very expenses lenses. I keep my EF lenses because I still shoot most Landscapes with a 5DS R and the RF lenses will not work on that camera.

I own a 5dsr that I use for everything. It is a great camera that produces wonderful images. However you will need "L" quite lenses to take full advantage of the sensor. Do not sell the 135 f2 lens. It is a fantastic lens particularly for portraits, although I use mine for some landscape work, in addition to portraits. I recommend the Canon 24 - 70 F4L as a walk around zoom lens or perhaps the 24 - 105 F4, if you need the extra range. The 24 - 70 is smaller and lighter and has Macro capacity.

Hunt's camera has some Canon Pro 10 printer with a good rebate. The printer is no longer in production, but it is an excellent printer. I have used mine for many years. Check it out. https://www.huntsphotoandvideo.com

If you really want 30MP in your price range I think the camera to look it is the Canon 90D. However The Rebel 7i and 8i are really good cameras in a much lower price range that will give you price space for good lenses. They use a sensor around 24MP and are very good cameras and easy to use. With plenty of features.

I would not purchase a new camera. The 6DII shoots at 6.5 frames per second. That is plenty fast enough for the sports you are shooting. It appears that you also shoot a fair amount of portraits. I would spend your money on a good prime for portraits. I use a Canon 85mm 1.14 and a Canon 135 f.2. They are each excellent portrait lenses and I think either one would meet your shooting needs better than a new camera.

I shoot with a Canon 5dsr. The camera has a setting that allows me to set different aspect rations and shows lines in the viewfinder that match the ratio. The captured image includes the full size of the sensor, but the lines are drawn on the down loaded image. I do not know if this option is available on other cameras. Here are the ratios I can select:
6:6 : Aspect ratio 6:6 3:4 : Aspect ratio 3:4 4:5 : Aspect ratio 4:5
6:7 : Aspect ratio 6:7 5:6 : Aspect ratio 10:12 5:7 : Aspect ratio 5:7