I'm glad you like my world
Tonguez:
Your character's homeland can be wherever you want it to be. A small offshore island is fine by me, if you like.
The status of half-orcs is that though they are derided as slow, ignorant, and stupid, their great strength and fighting ability leads to high demand for them among armies and navies. Also, their somewhat barbaric habits and their superstition are rather large barriers, in terms of becoming accepted as just another person. Half-orc mercenaries and half-orc "Tars" (common seamen, most Half-orcs are prevented from becoming ship's officers because of their natural slow-wittedness, theough there have been notable exceptions.) are very common, and often respected for their strength and fighting ability. So they are respected mostly on professional terms, but are often considered an inferior race, socially speaking.
If you want your Half-orc to be a Navigator type, he/she will be rather a special Half-orc, and may be subject to ridicule by other ship's officers until the character can prove himself/herself.
The tattoo is a really cool idea. That is definately allowed.
Answers to other questions:
Prof. Navigator includes both "naked eye" and instrumental navigation, but trying to navigate without the right instruments (charts, sextants, chronometers, etc.) will incur a rather hefty penalty.
Prof. Navigator and Prof. Pilot skills are different in that the ship's Pilot is the helmsman. He is often very skilled at steering the ship, but typically does not know how to plot a course. He can steer a course that the navigator tells him, but he typically can't plot a course. Often the Pilot is a common Tar. The Navigator, on the other hand, knows how to plot a course and find latitude, longitude, etc., which is often Greek to the Pilot, but he isn't typically very good at actually steering the vessel.
As a side note, characters possessing the skill Prof. Navigation often have a "leg-up" so to speak, if they want a position as a ship's officer. The Navigator on board a ship is generally either the First Mate, the Second Mate, or the Captain. Few vessels can afford the pay and upkeep of an officer who does nothing but navigate.
As to whether the Sailor skill is necessary even if you have the Navigation skill, I'm afraid it is. Otherwise, you're character may be the best navigator/pilot in the world, but they'll be seasick every which way, and they won't know a mainmast from a yardarm. I'm not forcing to take any particular skills, of course. What skills you take are purely your choice.
The Starlight spell allows you to navigate in any conditions. I.e., you could take a sight with your sextant even in the pitch dark, in a storm, if you have the Starlight spell.
Hope that helps.
I'll post the remaining setting details either today or tomorrow.