Goss - Yes, thank you.
Siiri - Excuse my brevity with these ones, I'm rushing on my way to work.
1. On the (very) rare chance that a child is born with a physical defect, how do the child's mother/family see it? What about the rest of society? How about becoming disabled from battle? How are amputees, the lame and the blinded (all from battle) viewed by the Myrian people?
Birth defects - This really does depend on the defect, but generally, this defect is seen as a weakness that the one who has it has to work much harder to overcome and still contribute.
Battle disabilities - Those injuries that come in battle, provided that they weren't because of some stupid mistake that they made (which would likely lead to others teasing them about their folly) are generally respected - battle is battle, and sacrifices are expected to be made.
2. Do Myrians only mate amongst themselves? If yes, won't this cause recessive genes and weaken the race? Or can a female choose from someone outside their race to impregnate her? What about male Myrians?
Generally the Myrians stick to their own kind. But it really does depend on the individual's preference and location. A Myrian in Falyndar with her family would likely be nudged towards a suitable (Myrian) mate. A Myrian outside of that influence could well choose someone she finds attractive. But it's really up to the individual. There are some hybrids running around Taloba... but they are seen as being 'not quite one, not quite the other', and there is some scorn involved there, as well as stigmata that comes from choosing a different race.
Males can. They have a little more freedom in that regard, obviously, since if they did impregnate a non-Myrian female, they don't necessarily have to stick around to raise it.
3. When choosing a life partner, is it mutually agreed upon by both parties or do the females "choose" and the males really have no choice? If it's not too much trouble, I'd like to know more about the dynamics of romantic relationships among Myrians (if it exists).
It's generally mutually agreed upon. I mean, sure you might have some females that are more insistent than others, and will pursue the one she likes until he eventually gives in or she loses interest, but it does depend on the individuals. The elders don't really interfere here - they leave this up to the individuals in question.
I'll edit this after I get home from work to add more (re: dynamics/relationship).