I apologize for the wall of text, and for the fact that I'm not giving an official response, just my personal understanding of things.
1) Extended Arcana has not been released yet, as far as I know.
2) The dwarf and gryx traits don't specifically mention it, so by RAW, no. However, you're the GM of your game. Whether you feel it's appropriate to make those races sink like a stone due to their increased density (because: SCIENCE!), or let them ignore it (because: FANTASY!) it's your call.
3) Yes, it is possible to buy just one lesser blood talent. In fact, I highly recommend humans trade up from skill specialization to something worth 20 or more points (personal favorites include "Nightvision," and "Hardiness" or "Amphibious Action" from Folklore). Given that these sorts of traits might remain for generations after first introduced to a family, and might go dormant for generations thereafter before popping back up again, it's even possible your character might not know why he/she has this trait, simply assuming he/she is good at what they do, or perhaps even blessed by whatever gods they worship.
4) I agree the whole issue of fatigue is poorly done in this game, but I think the basic assumption is that you treat your CON bonus as a minimum of +1 for that table.
5) Unarmed Strikes are Small-sized attacks, by default. The monk's level 1 bonus improves this to Medium, as does the "Martial Arts Training" Talent (10 DP, you can find it in HARP Sci-Fi, if you have access to that).
6) RAW, any two weapons can be used, so long as each weapon can be used with one hand. That said, Martial Law clarifies this slightly, explaining that the style in the core book is intended for use with two different *types* of weapons, not merely two *different* weapons. To support this spurious ruling, ICE then added another combat style called *paired weapons* that has completely different effects. That said, I personally don't see any valid rationale for saying you couldn't specify two of the same type of weapons, aside from their "Oops, we goofed! Hey! Let us distract you from our mistake with this shiny, new, underpowered option over this direction!" move.
7) Correct. Regardless of what your profession is, Universal Spells key off of Re/SD.
All of the polearms are listed below, but you're right in that the ones which can be used with 1 or 2 hands is not specified. To be honest, I would say to simply use your better judgement. Spear-and-shield styles have existed in the real world for thousands of years (watch 300 for a good example). That said, I would not even attempt using a halberd (an axehead strapped on the end of a long spear) with just one hand.
Incidentally, the javelin is a Medium weapon, regardless of whether you use it with 1 hand or 2.
9) Whatever you, as the GM, feel is appropriate. If you want, this could be some sacred relic that casts a healing spell once a day when needed to save your life (Major Healing is a good choice, or perhaps Lifekeeping). I personally like the idea that this comes in the form of a "Get out of Hell, free" card from a Monopoly game, personally signed on the back by the god of death.
10) You can use a focus or not, that's your option (this gets fleshed out in College of Magic). Ultimately, it's your choice whether your mage waves around a wand or wiggles his/her fingers. The special starting focus item is a particularly well-made one, thereby granting a bonus to casting your spells. Think of it like a bonus item, where the bonus added is to your spells, not swinging a sword or picking locks or whatever.
11) The cost of training packages gets rounded up.
12) As I've said before, if you're the GM, it's your game and you can rule however you fell is fair. Speaking from personal experience though, trying to move acrobatically to land in a better position after a fall CAN put you in a worse position than if you had simply fallen normally.
13) Getting attacked from the flank is +15, but can apply parry modifiers. Getting attacked from behind is +20 (5 more than getting flanked), but also parrying is not an option without special abilities or circumstances. It's that "and you can't parry" thing that really makes getting stabbed in the back so dangerous.
14) Yes, plus the cost of hiring a more skilled armorer, if necessary.
15) Yes, it means the enemy can attack you. If you don't disengage, the enemy can simply follow you and strike again immediately (check the "move & attack" and "press & melee" options for examples).
16) Never had this come up in-game, so I'm not sure. My guess is you have multiple stun effects running separately, each on its own timer, and you suffer the effects of being stunned until you shake them all off. In short, I believe its a binary state: yes or no, although there can be more than one reason for "yes" to apply (a spell and a blow to the head, for example).