1. Natives and other characters native to other parts of Ravenloft are going to confuse you for a caliban or worse because there are no native orcs. Since they don't know what an orc is, they can't recognize you for what you are. Outlanders that are familiar with orcs should be able to tell the difference, but I wouldn't exactly expect a better response from those that meet you for the first time. Orcs are looked upon with extreme but well-earned distrust.
2. Honestly, I'd have his Int at least at 8. My hellhound familiar has 6 intelligence to compare with. Even a typical orc has an 8 Int and since half-orcs have a -2 Int modifier, it means that you are below even a half-orc's typical intelligence level. Saying that you are dumb compared to even an orc is pretty bad. Below an 8 Int, I'd expect you to have a hard time even speaking a sentence. An 8 Wisdom is also typically below even the humanoid norm. 7 is the stated typical of an orc, but a half-orc does not have a negative modifier for wisdom, meaning 10 is the norm.
Here is an example of humanoid average intelligence levels -
6 - Ogre, Hill Giant, Troll
7 - Minotaur
8 - Orc, Half-Orc, Ogre Barbarian
10 - Goblin, Kobold, Bugbear, Hobgoblin
Here is an example of humanoid average wisdom levels -
7 - Orc
9 - Goblin, Hobgoblin, Kobold, Troll
10 - Ogre, Ogre Barbarian, Minotaur, Hill Giant
Honestly, I think the hardest thing to play in D&D is a dumb character. I consider myself a bright individual and I have a hard time dumbing down enough to play someone with a subpar intellect.
3. Your point of origin has nothing to do with quests, but affects how NPC's respond to you.