Hi Mike, Alex is right the placement of a tatt will just pop into your head one day and you'll know exactly where it is meant to go.
You've got plenty of time to have a good think about. A good trick is to get a copy of what you want and enlarge it to different sizes then you can place then around your body and see how it will look before it's permanent.
Also a good idea to see how it looks in different colours other than traditional black. Reds and blues can always give things a different look.
Hi Humayan, the small of your back is ok, it's when you get near the kidneys that it starts to tickle.
As for the ribs down the side
that really tickles.
Cheers