pinyin is quite literally a direct 1 to 1 with characters. It just uses phonecian letters to represent the sounds and those convert directly into the character. Like if i want to type 中国 which is China or more directly "middle kingdom" i literally type zhongguo on my keyboard and it is converted into the characters automatically. Also there are mutliple characters for each series of letters like 种过 is also an option for zhongguo. That is because different characters can use the same sounds. Some in different tones, and some in the same tones. But typically it will select the most common one for you, and also give a list to select manually which youd like.

When writing in pinyin itself you need accents to show tone, but when converting to characters you don't. Since the character has a tone. So usually you'll be typing in pinyin, and reading in characters.

I don't know anything about Japanese, but hanyu pinyin is CPC-approved! In fact, they teach children to read it early on in China. It doesn't take that long to learn how to read it.

Now, stinky awful wade-giles and other romanization is a whole other story

I ended up finding it a bit wonkier when learning it for the first time (e.g. 'shui' rhymes with 'wei', 'jiu' rhymes with 'you'), but it's just as consistent once you accept the orthographic idiosyncrasy. Edit: with respect to pinyin, only took a brief look at Wade-Giles and it feels a lot less sensible in comparison.