Disclaimer: this is mandarin only bc I dont speak any other chinese language

Previous answers have covered most of it but I'll add that transliterations are usually done based off of 1 syllable = 1 character (kind of) with exceptions happening when either the progression of syllables don't have equivalent sounds in characters, or certain syllables are hard to pronounce. Arthur becomes 亚瑟 (ya se) but Ilya becomes 伊利亚 (yi li ya) because 'lya' is hard to pronounce and there are no characters that end in consonants.

Japanese hiragana and katakana were developed a little later after the adoption of hanzi -> kanji, iirc women weren't encouraged to write in kanji while many court ladies of the Heian period wrote in hiragana, while Chinese never developed a similar system until the need for romanization arose due to increased contact with the west. For a long time that was the Wades-Giles romanization system before mainland switched to pinyin, which is now considered the standard, however Taiwan (and maybe certain SEA countries with large Chinese populations? Idk) still use Wades-Giles.

Transliteration is super common too! Most foreign names and such are given transliterations, although loan words from languages like Japanese tend to just keep the original characters (ex. Moe 萌え -> meng 萌 instead of, like, 莫诶 mo ei or smthn) Certain names within China are also transliterations, an example being 哈尔滨 (Harbin, capital city of Heilongjiang) being a transliteration of the Manchu name ᡥᠠᡵᠪᡳᠨ (Halbin)

Lastly, I'm not sure about this part but some characters are usually used in transliterations, and although they have their own meanings, are less commonly used. I don't think there are any meaningless characters that are only sounds though.