Chords and Vocals

I just posted my first song

writing it raised some questions about guitar and vocals

1)
what these boil down to is where does the melody line sit in the chord

for example in Jame's Drivers blues the fisrt chord is G

I would take as the starting point for the melody the open G on 4th string

the G on the bottom string is a bit low for me

is that how most  people pitch the vocals

 
2)

second is about composing the melody

my broad approach was to find a chord progression in my vocal range and which was appropriate for the subject of the song so I choose Am and some chords in the Am key (partly using theory and partly by ear)

but I didn't then have a melody

by trial and error I came up wth a tune which fitted the chords (its sort of the chords but wobbles around  a bit more)

is that a sensible approach