Nothing bad - those are totally normal. Some of my Hoyas get them too, and it seems to be a characteristic of certain species, because the same species keep popping up with this question. (Like in this thread here). Hoyas will also get black dots from sun damage, (often after being misted), on their tops. And spots can, of course, mean fungus or pests. But the kind you've pictured are innocent. You will notice, as time goes on, that there is no browning or yellowing associated with these - as would be the case with "bad spots." In some plants, they go away as the leaf matures, but I don't think my micrantha ones go away, or mitrata, and many others I can think of. I think they're quite pretty. Enjoy!

I'm guessing that your description just doesn't suggest anything to any of us, sorry. One of those times when images would be helpful. A serious whitefly infestation is a most difficult thing to deal with, especially if it is community wide, as you suggest. Some gardeners like the sticky traps, but they can also catch beneficial insects and animals, too. I don't like them and won't use them....unless in a greenhouse.

Do not use soapy water - I know it is often recommended, but it dissolves wax on the leaves...the only soap to be used on plants should be true vegetable-based Castile soap (olive oil based). I do not have experience with neem oil, so can't comment. Lots of marks appear to be oedema (the hard, black bumps), even the bigger dry-looking patches. That happens when plant cant transpire all the water received. Other is possibility of powdery mildew, encouraged by high humidity. What kind of soil/mix is it potted in? Where is this plant kept? How much sunlight is it receiving? Even if you say it dropped lots of leaves, it looks quite etiolated - spaces between internodes are too big. That suggest not enough light. I would also suggest potting plants higher in the pot - the soil level should be higher. That will also help with soil drying up faster and general air circulation that is also important for succulents.

Appears to be spider mites. Nasty critters. I've tried the high price mite poison. They damage the plant and the s mites will become ammuned after 2 apps and then you need a different one. Finally I found a good answer. Dishsoap. It must be the gentle type. Some are degreasers. Too strong. Ivory is good. 1 ounce to the gallon. Spray throughly, top and underside. Re-do in a week. Watch it it may need a third app. I think the spider mites are still active. Good luck