The adequately sized vacuum chamber arrived today, much more quickly than I expected. Initially it would not seal and I could see no holes or leaks. But when I removed the silicon gasket I found a small silicon flake which was the problem. Thorough cleaning, and all was well.
With this arrival I am almost fully equipped to start casting. So today I built 2 trees.
Preparing the moulds, and the metal pour will probably occupy about 10 hours, so I will need a totally free day. Maybe Thursday.