DON'T dust the blueberries. If you are on neutral soil, they'd rather have some sulfur on the soil to acidify it. And if you are on neutral soil (except for some rarer types) it is hard to imagine you have any calcium deficiency or need to raise the pH further.

No, none of those are really DIY-able without at least taking some classes and putting in a lot of practice time. But then, for the vast majority of the population, neither is regular plaster (as opposed to glopping joint compound around, a peeve of mine). Real plastering done right is an art form IMO, and skilled plasterers make it look so easy when it isn't! And yes, it is expensive, especially the Tadelakt simply because there are so few practitioners in this country. I imagine the pool-plaster method is probably the cheapest way to go.

Hi. Yes, these plants are all susceptible to a high PH, perhaps buy a cheap kit and check, the presence of a high soda (High PH) soil is commonly not an instant death to many of the species you mention, unless it is extremely high, though they will be unhealthy and slowly degrade till they become susceptible to disease or insect attack, as PH rises (becomes more alkaline) you will notice a yellowing of the leaves, normally from the edges of the leaves and then moving inward over time, this effect is known as "Lime Chlorosis" I have seen a Isopogon growing in the middle of a fire trail with a blob of concrete that had been dropped on it and set there, the plant was stunted and yellow ... but was not dead and survived, I would wonder if a "Native Garden Hater" had not "Glopho'd" your garden? however, dust from gyprock is severely Soda and I would imagine could kill plants quickly, but as we have had so much rain (I do not know where you are from) I would think the dust would have been washed through evenly and a slow degeneration of health would be noticed, not sudden death, perhaps you have a fungal problem, perhaps Phytophora, check your gardens soils ability to drain, pull a a dead plant and see if the roots are black, especially around the point where the soil covered the roots/stock of the plant, the addition of iron, in chelate form initially, but it's effects are short term and you will need to keep applying it at rates to apprehend the problem if it is a PH related one, there are other forms of iron that last longer, but chelated iron works quickly, Lime locks up nutrients, and many Aus natives are not adapted to extracting nutrients in such a condition. Good Luck.

I assume you mean a faux Venetian plaster that is a thin coating over gypsum wall board. The paper facing on standard gypsum wall board doesn't accept a veneer plaster finish coating well. For that you need a veneer plaster "base" commonly called "blueboard" because it has a light blue/gray color. Any drywall contractor will know what it is. Veneer plaster is common only in a few parts of the US. Where is the project located?