The decision as to whether mass screening is justified or not is complex, and varies a lot by test/condition/population etc. Luckily there are lots of smart people whose job it is to do these caclulations.

In your list, 1-4 are common enough, the tests are accurate enough, the costs of intervention are low enough and the benefits of early intervention are high enough to justify screening, which is why they do generally screen for them at least in hgiher risk groups. The other two are more mixed, which is why mass screening is less common.

All the evidence for full body scans is that they are not justified for asymptomatic people. The false positives are high, the costs of these false positives are high, and the imporved outcomes are too low to justify them. If you want one, go ahead, but realise that almost anything it finds is likely to be false either positive or not likely to ever cause a problem, and you'd have to deal with the worry and invasive tests and even surgery in aid of something that may never cause any trouble.