I am just in the learning stages for arranging like you.
I have worked with my music teacher and she guided me to put chords into the melody where there were whole (semi breve) and half (minim) notes.
Then go back and check against the piece of music – to see that they match vocal emphasis or long notes.
Hey Miz. Thanks. That emphasis is like a validation of what I’m intuitively thinking as I arrange. I start by placing down all the vocal notes. Then I play it on the uke to make sure I have the melody correct. Then I start experimenting with a chord containing that note (usually it’s just holding down the melody note and strumming the correct open strings). I can almost use a chord for every single note this way but I figured it was overkill.