In bar one, should I write chord I twice or should I write I_________ Also, in bar 3, am I right if I added chord symbols to each of the last three notes or should I add it to only one?
There's no universal answer for how to write the first measure. Plenty of people (myself included) would just write
Iand not write anything else until the chord changes, the assumption being that the chord stays the same until we analyze another chord. People will also write
I Ias you did, and as you said another possibility is
I ----. All are correct.
It's very common for chords to change quickly right before the end of a phrase. (In fancy terms, we say that "the harmonic rhythm accelerates as we approach the cadence," but don't worry if you haven't heard those terms yet; you will later!) Furthermore, your chords make complete sense there, so the end of your m. 3 looks great to me!
(Note: People typically use lowercase Roman numerals for minor chords. If that's the case, make sure you write your
II as a
ii. But if your teacher has asked you to use all uppercase Roman numerals, then stick with