a)The whole weapon cord thing is cheesy to me, but when in Rome...
I) As far as I can tell, the free action to throw has nothing to do with proficiency. It's still a free action to pull out an arrow for a longbow even if I'm not proficient.
II) I can cast with only one hand, so it shouldn't be an issue. I could have a longsword or even chop off the hand and replace with a hookhand and cast without issue with the other. IMO the whole spell fail for shields is kind of silly since you only need one hand. If this is an issue, I could always drop the shield and pick it up with my tail for the same quick action. The weapon cord just has a limit on where the shield can go(adjacent squares).
III) The only thing proficiency in the shield does is let you ignore the armor pent. to your attacks. Since darkwood takes the pent. to 0, she gets a 0 pent to attacks, so it's not an issue.
b) Bite from merged form, claws from tiefling.
c) this isn't what the synthisist page in your wiki says. "Can a synthesist (page 80) make attacks from his own body (such as manufactured weapons, unarmed strikes, or natural attacks) and attacks from the fused eidolon in the same round?" = "Yes, but the fused character's natural attacks are still subject to the Maximum Attacks entry in the table for an eidolon of his level. For example, a 1st-level synthesist is limited to 3 natural attacks per round, whether those natural attacks are from the eidolon, the synthesist, or a combination of the two. "
D) again, your wiki says I can get both attacks (claws and bite). My only other option for ranged damage that adds str damage is sling. crossbows have a longer load time and have a lower minimum damage, so I'd avoid those unless I KNEW I'd be dealing with long ranges.
e) oops, That I can fix.
f) I took tiefling because the wiki synthysist section said that I could use both my natural attacks AND my merged forms attacks. It's a savings of 1 evolution point and I still have a good enough stat to cast my highest level spells. I don't need my stat bonus to most of my spells as I either heal myself or summon creatures and neither one needs a save. I plan to stay in merged for all day so stats of 14/14/12/16/14/16 looks like pretty sweet stats IMO. I'm really only losing 2 summon monsters SL abilities, and I don't want to be in humanoid form anyway.
So to add it all together:
The shield is a cheesy but IMO RAW way to avoid spell failure. I'd only use it for a few levels, so it wouldn't be a big deal if you said no. The only thing I'd ask is that you let me know why it doesn't work so I can avoid it in the future. For the bite and claw, I've already quoted the section from the wiki that says both attacks should work. see
http://livingpf.wikia.com/wiki/Synthesist If this wiki is in error, let me know what is different and I'll have to start the character from scratch as I based the character on it being correct.
Quotes for shield: "Nonproficient with Armor Worn: A character who wears armor and/or uses a shield with which he is not proficient takes the armor's (and/or shield's) armor check penalty on attack rolls as well as on all Dex- and Str-based ability and skill checks. The penalty for non-proficiency with armor stacks with the penalty for shields." + "This shield is designed for throwing and has specially designed straps that allow you to unclasp and throw it as a free action." + "To cast a spell with a somatic (S) component, you must gesture freely with at least one hand."
EDIT: Fixed skill. I'd put a point into linguistics and added my extra language but forgot to add the rank to skills.

EDIT2: Just thought of something else with shield. I could unbuckle the shield and just hold it in my one hand. As a weapon held in my hand it has no spell failure (it's no longer being worn). Then I could use my move to rebuckle and not have to use weapon cord.