Good luck with your repairs Katherine.You have raised many questions.
The autoclaved lime I have never used, but I have heard that it is very strong in plasters and mortars, and, as you write, it is usable immediately. The gauging plaster is a US Gypsum product available from specialty suppliers. If you are really interested in becoming a plasterer you will have to read some books, take some courses, and hang out with some experts. Be forewarned that this is the most physically demanding of all the construction trades but the most creatively rewarding - yes even more than painting. You might have to get a quote for your cracks, this is a job requiring experience. I just fixed extensive cracking in a 1912 building, you never know what you will find underneath the top layer.
You will have problems at 100% lime, because the lime will shrink slightly - this is why we add sand for fresco, or gypsum plaster for decoration (gypsum slightly expands). My own mix for fresco is often high calcite lime putty, white dolomite/marble sand (of various sizes) and white cement. This is tricky because white cement also shrinks. I am also using concrete bonder, a type of glue from stucco suppliers, it is used to make sure the layers stick together and onto metal lath. I was worried that it might interfere with water flow between the layers, but I have found no difference in side by side tests. I try to make sure that the bonder is limited to the surface, that it does not become mixed in the general putty. I am interested in exterior frescoes, that can go out in the gardens in summertime, under cover for the winter, so I am more concerned with long term wear. It is amazing how tightly the pigment bonds to the lime - I have had some painted scraps underwater (!!!) for three months now and the colors do not wash out and the cured sand/putty (no cement in this one) still stays together - amazing. I think the biggest killer of outdoor fresco will be frost - freeze thaw damage.
A lime by itself would have to applied like a paint over many years - this is like the Greek villages where 1000's of years of an annual lime paint have built up a hard thick shell.
To all those who asked for scans of lime paint recipes, please bear with me, my scanner is down. I might just send it to Ilia in PDF format, via email, and let him figure how to post it. I have many more old recipes too.
