It's not just the "levelness". It's the support under the floor that keeps it rigid. Any flex at all, and it will crack. It doesn't matter if it's smooth and totally level. It's all about your joists and subfloor. Your joists need to have the right spacing, the right depth, and not span too long of a length. Plus the subfloor needs to be the right thickness. A lot of time, this add considerable height to the installation in order to add rigidity. Your expert should be fully knowledgable about how to do the math to calculate whether or not your home can support such large tile without cracking. If he doesn't mention or understand how to calculate your existing space's deflection, then he doesn't know enough to do the job. Period. Move on to someone who does know how to figure this information out. Or, perhaps DIY it with the help of the pros at the John Bridge Forum.

No idea how much to suggest for you to use, but we salted our pool and used water softner pellets by just throwing them in and playing in the pool. Took about half an hour for them to dissolve. Just be sure that your salt source has nothing in it but salt. Some softner salts have other "stuff" in them.

I have it on my own house. It looks fine and gives the house am appearance that makes it stand out from others with traditional double 4 siding IMHO.

This Neff oven (example) runs on 220-240 volts at 60 hz so it should be usable out of the box. The problem would be buying it and having it shipped to the US; and, of course, there would be no one here to service it if it broke. Interestingly, Neff is a wholly-owned subsidiary of BSH which also owns Bosch and Thermador.