Hi Jonel
It's been a while since my Theory was in shape, but I can remember a bunch of stuff, and how I felt about it.
You don't need to begin nor end on the tonic, to make a good melody line, many really famous players can't read the dots, not what an interrupted cadance is. Can you imaging Hendrix saying to Noel Redding, "Man, I think you need to play an alberti bass on that one, dude..." In fact on many recording hendrix play the bass himself, while Noel stood outside the studio with a fag on.
So many great songs can be theortically analysed post recording, and it's amazing to hear how they have been constructed, I heard one bloke dissect A Day in the Life by the Beatles, and boy was it complex...
One of the reasons I learned to read music was so I could write down and not forget my compositions, but a benefit I didnb't expect was to to appreciate structurally what was going on and what would fit when I'm soloing/improvising.
Back to your question...
Your notes do not need to be in the starting chord.
For example if you start off a blues number with a regular C E G, your Tune could start with a Bflat (the 7th) of the chord of C7, so effectively you are extending the chord on which you start, or a 9th, 13th etc. depending on the colour you are after.
Hope this helps
cpm