Hey Richie, when picking a camera there is a lot to be considered. Usually many questions are asked about the purpose of the camera, etc etc etc. However, given that you want to shoot wide-angle and fisheye, that narrows down the best options for your use case considerably.
When photographers choose to shoot primarily wide-angle or fish-eye (ULTRA wide-angle, really) they will choose to go with a full frame camera. The reason this is, is due to the "crop ratio" of the smaller sensors. Smaller sensors like APS-C add 1.5X focal range to your chosen lens. Hence a 20MM full frame lens will really be a 30MM lens on an A6600 or ZV-E10. If you are looking for the sharpest lenses they come in full frame, and than you have to equate for the crop factor. This makes shooting wide-angle photography incredibly more difficult because you need much wider glass to get those pristine wide-angle shots.
The A7SIII is a fantastic camera for ultra low-light photography and low light video (as well as 120P/4K video). The only drawback is that the still images are 12MP. This means there is not a lot of room to crop in if you need to. The more MP you have, the more room you have to crop and reframe. Adding a degree of flexibility. If it were me, and I wanted wide-angle shots for general landscape purposes, I would choose the A7IV as it has excellent low light capabilities and is a full frame capability. It also gives you 33MP and a rotating screen. An A7RIV is a great camera as well, not the best in low light, unless you are used to having a tripod with you at all times. This is also a FANTASTIC option for wide-angle landscape. The A7IV offers more flexibility for those wanting to jump into photography feet first.
You can see what lenses are compatible with different bodies at this link https://support.d-imaging.sony.co.jp/www/cscs/lens_body/
If you get a full-frame body, they use Sony FE lenses, the G-master lenses are generally the sharpest but the other G lenses are stupid sharp as well.
