Sony Alpha a7R IV Mirrorless Digital Camera with 24-105mm Lens and Accessories Kit

An upgrade to the A7R IV would be worth it based on the higher resolution it offers. This particularly good for those looking for the highest possible image quality for publication or enlargements.

Just as those lenses will perform at different levels of quality on a 24MP sensor, they will perform at different levels on a 61MP sensor. There's no objective line that you can draw to say this lens will perform adequately and that lens won't--it's a subjective decision that each photographer needs to make. Better lenses will perform better, on 24MP or on 61MP.

Any small-ish camera can overheat when shooting 4K video in a hot environment, but the A7R IV is very unlikely to overheat.

Batteries, no. Memory cards, yes.

What Jeremy has noted is probably true - but in the work I do, I have not had any such issues.

Sony does not have an AC adapter for the Sony Alpha a7R IV Mirrorless Digital Camera but there is is the IndiPRO Tools AC Power Supply with NP-FZ100 Dummy Battery. Here is the link: https://bhpho.to/2ON8q0v

Hi--the A7 III performs almost to the level of the low-light video king, the A7s II, so if low-light video is the most important aspect for you, the A7 III is probably the better option, although if you shoot in Super35, for instance, you will be getting images with 10MP with the A7 III, but 24MP with the A7R III. The A7R III has great low-light performance, but not quite at the level of the A7 III.

I don't have aps-c lenses so do not have first hand knowledge. It probably depends on the focusing speed of the lens you use. Cheaper lenses without fancy focusing motors will be slower than G or GS lenses. Other than that why should it. Smaller files will make recording, downloading and processing faster.