I have 13 overall (after 20+ trips and combining some - I lost my individual number).
If I come to work in long sleeves - you wouldn't know. Most of the time people miss the celtic "A" on my inside right forearm (about 1.5" x 1.0").
All the others are spread out - left upper arm band, right shoulder blade, left calf ban, left foot, right ankle - and so on.
My father's only advice (other than nothig repulsive - most of mine is tribal/celtic/lettering) - other than the inside forearm, which was my first - nothing visible. Don't cut yourself off professionally (and to an extent socially).
Keep it someplace you can see it (for newbies - keep them off your back - you'll forget about it).
The calf is cool - but hope you like some pain.
Hipbone will "tickle" too.