While we’re speaking of large numbers, I’ve finished reading that section myself, and I must say I found the explanation of numbers over 10,000 to be a little too brief. Perhaps an extra half paragraph and an example is necessary.
The explanation currently there says that (for example) 1,000,000 is ひゃくまん and 10,000,000 is いっせんまん, which (if I didn’t know better) would give me the impression that 11,000,000 would be いっせんまんひゃくまん, when in actual fact it’s いっせんひゃくまん. As in, just as we’d say “eleven million”, in Japanese they say “(one thousand, one hundred) ten thousands”.
Mind you, I also thought that one thousand was always just せん, not いっせん. And he switches from using きゅうじゅう for 90 to くじゅう without comment. Same with くひゃく. I was taught that one of these was used more often, but I never could remember which.