What are the exact dimensions of the unit, please? D 554 X W 431 X H 88.4 mm?
I'd like to know this as well. It's not listed on the website as far as I can tell.
Will there be any problem with plugging SP30 to 230v 50Hz mains socket?
230v 50Hz should work nicely. You'll likely need one 20 amp circuit or two 15 amp circuits at 230v for each SP30.
You don't really need a rack. The SP30 should run just fine lying on a table desk, shelf, or the floor, as long as the surface it's lying on won't get damaged by persistent temperatures up to 80°C. A rack might improve airflow a little bit, but it's optional.