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Having trouble with front squats:

a) how to hold weight on shoulders/collar bone so that it doesn't feel painful
b) can't stable weight on shoulder/collar bone
c) arms are not parallel to ground
d) how should the back be

the reason i need to learn front squat is that all this heavy high bar back squat is making my lordosis / anterior pelvic tilt worse.

It does help, but the main problem with my front squat is that i have kyphosis.  It has to be tough to front squat when you have arch/rounded back.

I have kyphotic posture too. And i am also 6'' taller than you so i imagine that makes it even worse for squats ( more lean ).
I had problems front squatting, when reaching at the bottom , lean + kyphotic posture made the bar fall , even empty bar. When i got my lifting shoes , it auto fixed , suddently i could do perfect front squats.
But now i can also do them in flat shoes, so who knows, maybe it was mental. If you have enough mobility/flexibility to hold the bar like in a clean, you can afford some lean and have the bar safely locked.
Try to progress it slowly and see what happens, start with empty bar and keep adding small weights until form begins to break down.
Also you might want to do some thoracic/shoulder mobility work, it should help your posture.

Then how about working on fixing that? I am no mobility expert but i am sure there are speific things to do to get there.
LBSS?

http://www.youtube.com/watch?v=_LYNgODd7eQ

Watch the finger placement. Front squatting imo is all about relaxing the wrists, most olympic weightlifters have one or two fingers behind the bar when front squatting. The painful feeling on the clavicles will pass, stick with it, and stretch those wrists! And if that doesn't work you can still use straps using the poliquin method

Front squatting imo is all about relaxing the wrists, most olympic weightlifters have one or two fingers behind the bar when front squatting. The painful feeling on the clavicles will pass, stick with it, and stretch those wrists!

+100

No, trust me... it's impossible. There's no way these elbows come up if I still want to have a neck, head, etc.

Oh come on , give it a chance. We didn't suggest you to become Nadia Comaneci, just achieve a mediocre front squat locking position.
Also , how about the cross-arm grip?

One thing i've very grateful about is how Lance was encouraging early on with my front squats when my form wasn't very good. I kept up with it and my flexibility and depth improved with time and eventually it became a very natural lift for me. It felt natural even from the start which is why I persisted with it but looking back initially my depth was high and I wasn't very upright. So my suggestion is to just do them, even if they're imperfect, as long as you're improving over time it will eventually come together. Just keep working at it.

When it comes to bar placement initially I took a wide grip, then in a few weeks time I could bring the grip in a lot (like an inch or so from the smooth). Flexibility improves as you do them regularly, so just start with what works for you and try to bring in the grip slightly over successive workouts.

Either you are the most imobile/unflexible or the most stubborn human alive.
  anyway, 

Haha, you tempt me to film at home with my bar (not an olympic bar but it will get the point across) trying all kinds of bar grips to see just how bad it can be. I won't even attempt to squat, just to keep the bar "on the shoulders" (impossible). The bar can only be held on the chest in my case. I have tried again and again, couldn't do it. That's the biggest reason why I haven't increase my clean too - because I can't catch a bigger weight than I'm doing now on the chest/arms.