I found my a7r2 less than perfect in focusing in some situations & upgraded to the a7r3. With the 2 cameras you mention I'd go with the a7iii for it's superior focusing capability.

I have used Lens Rental twice they have great to deal with.

l don't know about the other lenses but the 55-210 was a decent lens. However Sony has far more capable outstanding lenses. I sold my 55-210 and went with the 70-200mm.

I have the lens. It's great & it doesn't produce a squeak.

I have never been in Salem close to Halloween. However, my daughter lives in Salem. Expect parking to be difficult. Additionally they have lot of parades during the month of October. We were there at the end of June & they shut down traffic in the center of town for a parade that created a real problem for us getting across town. Salem is a great town to visit but it can be aggravating at times to get around.

Have the 70-200mm f.28 lens & just a couple of others. It is an outstanding lens and is highly recommended. Unquestionably, it is expensive. But that can be your workhorse & unless you're a professional you may not need much else.

The Nikon D500 gets stellar reviews for it's rapid focusing. I have the Sony a7r3 and it produces some beautiful images but does fall down at times focusing which is one of the negatives of mirrorless cameras versus a Nikon D500. Sony's answer is the Sony a9. Whether it measures up the D500 is a good question & perhaps someone out there with knowledge of both can give us an answer.

We were in Scotland on a cruise last year. The longest lens I had was 200mm which was still quite good for landscapes. The biggest problem
was the weather. The weather was mostly overcast and rainy resulting in a lot of mediocre shots.

We took this cruise with Princess a number of years ago. During the rail part we stopped in Denali National Park overnight. We did a tour of the park, that would be one area that would be great to be able to shoot again. Also College Fjord when we were on the ship. Seeing the glaciers was very impressive. For that location either side of the ship would have been okay but be prepared to move to the other side depending upon what's going on.

The Sony a7r3 produces great video even without using the 4k, the 4k is a bit of a plus but not the be all or end all.

I had it for about a month. I was using it with a polarizing lens at very fast speeds (1/1600, etc) out on the beach and found shots would come out under exposed earlier in the morning or later in the day (from 4 p.m. on) especially if the sun was behind the clouds. At 400mm the aperture is 5.6 & combined with the filter shots were being ruined. However, in the right situations it's a great lens.

Check out DxOMark's data base on lenses. This is a great resource.

Another lens- the 16-35 mm is highly rated by DXO mark. Check out all of the Sony lenses on the DXO website. I own the 24-70mm plus 70-200mm f2.8. Both are great lenses especially the 70-200mm. I have used the 100-400mm- it is a very slow lens, it's transmission score under the DXO system is very poor which shows up in early morning shots, etc.

FYI I just looked at my manual & I see the automatic photo review can be set for as long as 10 seconds. If it's holding longer than that you may have a problem.

I have a Sony a7r3 & have owned several other Sonys before that. Their cameras allow you to turn off the photo review. However, even if you have that feature on for the photo review it should only stay up for a couple of seconds. However, in your title you mention photo magnification. That's a different feature used for focusing. The camera may be set up to stay in magnification mode indefinitely. However, that doesn't sound like your problem if you are indefinitely seeing the photo you just took. If that's the case you may have a problem & should call Sony.