Need help choosing new camera & lens

Your name is very familiar to me because I too was a member of the Sony A-mount forum for many years. Like you, I had the A77ii and the Sigma 10-20mm, plus 2 more Sony lenses, one being the excellent 16-80mm. However I decided in 2018 that I had to move on and upwards before I expired. So I sold my gear and bought the A7Riii plus 3 lenses (see my list below).

I have never regretted the move for one moment. The transformation has been enormous, especially in AF, eye-AF, the improved ability to customise and of course pixel numbers. The combination of pixels and excellent image quality enables one to crop significantly without noticeably affecting print quality.

As for lens quality, the Zeiss 16-35mm completely out-performs the Sigma 10-20mm. Here is a comprehensive review that does not often find mention in these pages: Carl-Zeiss Vario-Tessar T* FE 16-35mm f/4 ZA OSS ( Sony SEL1635Z ) - Review / Test Report (opticallimits.com).

Don’t forget that the test images you see there are full-size and equivalent to about 7 feet in width. I feel from my experience that the review underestimates the lens’s quality bearing in mind that most people are unlikely to print huge sizes. As for the ‘softness’ of edges at 35mm that is often mentioned, I have carried out my own tests. While there is indeed a slight softness in edges at f/4, you have to peep at 100% to find it and it is almost certainly unnoticeable in normal-sized prints. By f/5.6 it is virtually undetectable and beyond that complete gone.

As a final point, I would thoroughly recommend the Sony 24-105mm lens. The quality it delivers is amazing and I find it fulfills my needs for at least 90% of my photography. And by the way I submit my work for competitions so my images are regularly subjected to critique by judges. Image quality has never been an issue.