Likewise. I tried 明日デートに行きます and it was marked wrong. I reported it (Oct. 21, 2017).

Very much agreed. It would be unnatural in most contexts to include the pronoun in this sentence (big issue across this course as a whole imo)

I think so. This is Duo first time I think(Am I right?)

i second that question.

From my understanding the "デートに行きます" implies "will go on the date" デートします is basically saying "it's a date" omitting the action of "going" on the date.

Ashita is close to today and when You're saying about tomorrow's event like in this example without adding a time when it will be taking place, You don't need to say は after ashita.

Same thing with a yesterday, the day before yesterday, next week etc.

は is a topic marker; essentially it emphasizes that we (as opposed to someone else) are going on a date.

I hope I said it right xd

The main thing is undetermined time determiner ex. "I will go on a date tomorrow" is right in this. But "I will go on date tomorrow at 6 six am" need は I think.

From what I read ikimasu is just the polite version

You wouldn't say deeto wo because deeto is not the object of iku: you don't 'go something', you 'go somewhere'. To express the direction, you need ni.

In this case, ni indicates the purpose. http://www.punipunijapan.com/japanese-particle-ni-purpose/