The は after 今日 is optional right?
In this case, yes. Not always. If you spontaneously mention that you're going to sing today, you can omit は. But if someone asks you, "When are you going to sing?" then your answer must include the particle は.
If it's an answer to "when?" it must NOT have 今日は! That's like changing the subject from when are you going to do it to what are you going to do.
Yes, though you might need to add a comma after 今日 instead of a particle in order to distinguish it from the following word.
Kyō wa uta wo utai masu
'Wo' is pronounced as 'o' here
Yes and no. It is more common to use the 'o' pronunciation, but I once new a Japanese person who consistently pronounced it 'wo'. I believe it's a matter of dialect.
I read that as "a new Japanese person" and pictured a baby talking to you
I like how they have to plan this out ahead of time like "ah yes one of my goals for today is to sing a song"
How do I know when to use 音楽 (おんがく) or 歌(うた) ? What is the difference between the two words?
音楽 is music. 歌 is song.
今日(present day/today)歌(song)を歌います。(to sing)
Just some random information:
If you want to find a cover of a song, search for 歌ってみた
What's wrong with 歌を今日うたいます? I thought the time descriptor could go immediately before the verb, without a particle.
It can go there, yes, but it is more common to place it early in the sentence. Doing it like this will put emphasis on the time. You can read more about Japanese word order at https://8020japanese.com/japanese-word-order/ .
I don't know if that's technically wrong, but it's still some weird-looking syntax.
Shouldn't "今日は歌を歌うになります" be Ok ? With the [infinitive]+になる。= "I will do [infinitive]"
It is marking me ascwrong for using the kanji instead of hiragana.
That Japanese is a bit better for "Today I will sing a song." Leave off the は for the sentence given. But Duo will mark you wrong if you do it here.