400#, yes. My mistake.
The Global stone is a decent combination stone, but by no means the best. It seems expensive to me at its US prices, and even more at its UK (assuming your link is representative).
I'm not trying to talk you out of the "ceramic" stone -- which is a waterstone by the way -- but be aware that there are prep and maintenance rituals involved with waterstones. They need to be soaked before use, then carefully dried after, and flattened frequently.
As to your question about jumping from 240# to 1000#. It's not too big a jump at all. Even though the Japanese are pretty good about reporting grit honestly and using consistently sized abrasive particles (i.e., well-screened), one shouldn't infer too much from grit numbers alone. There are other factors which determine how far down or up a stone can reach in terms of the next grit in sequence. For instance, an "Arashiyama" will reach down like a 3000# and up like an 8000#. So, no problem preceding it with a 800# - 1200#, and following it with a 12,000# - 30,000#.
The reason I suggested Naniwa Superstones is because of the amount of feedback they provide, and because they're so easy to flatten. They're among the best stones for a beginner. On the other hand, while I respect them, they wouldn't be a good choice for me. Of course the 10,000# is an exception... Which should give you an idea of how deep the subject goes.
I'd rate the Naniwa Combi, most of the King combis, and the Norton combi above the Global. I suspect you can find the Norton pretty easily in the UK. Here's a link to a European seller who has a decent selection of waterstones: Japanese Waterstones and other Sharpening Tools
Don't get shy about asking questions,