Does The Sight work through binoculars glasses(spectacles)/contact lens/magnifying glass/window/fog/mist/clear water?

I'd say that if the character thinks they can see, then they can see.  This is magic, belief MATTERS.

Okay, what Fred & Co may have intended for tagging, and What The Book Says differ here.

Allow me.

A tag is a special move that you may be able to
do when you’re invoking aspects other than your
own. Whenever you make a roll to gain access
to or create an aspect, as per the list on page 105,
you may invoke it one time, and one time only, for
free—as in, you don’t spend from your pool of
fate points to take advantage of the aspect.

Not "invoke or compel", not "use":  Just "invoke". 

If you look at the TOC of chapter 7 "Aspects", you'll see the following:

Aspects
  What Are Aspects?
  Using Aspects
    Invoking Aspects
    Compelling Aspects
  Using Others Aspects
    Invoking Others Aspects
    Compelling Others Aspects
...

So there are two things you can do with an aspect.  You can Invoke it, or Compel it.  Tagging can only Invoke.

Now, there are two kinds of invoking, there's "tweak the dice (reroll, +2 to an existing one)", and "Invoke for Effect".

You can also invoke an aspect for effect, using
it to declare a fact or circumstance that would
be of benefit to your character. This costs a
fate point like any other invocation does. For
example, you could invoke your character’s
Warden Connections aspect to declare that
there’s a Warden actually in town.

And Invoking Others Aspects says this about invoking for effect:

Invocations on other aspects can also be done
for effect, allowing you to use someone else’s
aspect or a scene aspect to make a declaration.
All the guidelines for invoking for effect (page 99)
apply here.

Allowing someone to invoke for effect to create a compel negates the differences between invokes and compels.  But there clearly is a difference.

So the RAW and Fred are different.  There's nothing wrong with that, but realize that there IS a difference.  Even if that's what Fred Meant, it's still not what The Rules Say.  If an Errata sheet or new version comes out that changes this, so be it... but DFRPG 1.0 has a specific meaning.

So based on my literal reading of The RAW, my players (should I ever get some... sheesh) would not be able to Tag a "gut stab" consequence for a compel, but could Tag it to declare that there's enough collectable blood on the scene to use for thaumaturgic targeting.

Craftsmanship:

Big Pocking Wrench: + 1 to Fixing & +1 to Breaking when Portella uses his Big Pocking Wrench.

(John Ringo "Empire of Man" reference)

Scavenger: -2 time shifts on Building and Fixing when you have access to equipment (functional or not) that might reasonably supply parts for whatever it is you're trying to build or fix.  Note: They don't work after they've been scavenged.

AKA "Kit Bashing"

Automotive Genius: +2 to all craftsmanship rolls related to cars.  This bonus drops off as you get further and further away from cars.  It might provide a +1 when working with a Semi Trailer, and no benefit at all when working on an Abrams.

NOTE: You can replace "Automotive" with "electronics", "chemical", "Sword smith", etc, etc.

Example 1: Joe Wizard decides to use Spirit magic to cause a blinding light to fill a zone giving all in it who fail their defense rolls, a negative aspect of Blinded By the Light.

Now I get that Joe Wizard can tag this or hand it off to his assassin friend to invoke against one of the NPCs for a +2 on, let's say, a Stealth roll or an attack roll. Joe Wizard could also compel NPC #1 to attack his best friend and lifetime companion NPC #2 (who bonded over having the same first and middle name).

Keep in mind that you can't use your free Tag to compel, only to invoke.  If it's sticky, anyone interested can start throwing around fate points for compels & invokes, but the free Tag may only be Invoked.

It also sounds like neither was spending fate points on their (or each other's) aspects.  When fate points start flowing it comes down to who has more points to spend and more aspects that apply.

there is the possibility in my game, that the gang - when it is just meant as an annoyance to the players - that they may only have a mild and a medium consequence.

Generic mooks shouldn't get any consequences at all.  And I Quote:

One reason almost all nameless and
supporting NPCs qualify as minor opposition
is because they do not fight to the end—they
fight until their stress tracks get bypassed and
then either concede or are taken out.

Emphasis added.

That section goes on to say that even main baddies might not go all the way to "Extreme Consequences" to further their ends.  They'll allow themselves to be taken out if they know the PCs won't kill them outright.  Failing that, they'll make a Concession: fell into a "nobody could survive that" situation, only to appear a few sessions later with some pretty new scars, and a Hunger For Revenge.

You're assuming (as is the player) that the "I chose Mortal" version of this character will be capable of Evocation and/or Thaumaturgy.

I would have expected them to become a Pure Mortal, complete with the bonus refresh.  I suppose it really depends on the mortal parent.