Question 1: Do you take Zahndrekh because you'd normally take all the "survival" gear anyhow, and you're only paying 5 points for Adaptive / Counter tactics, or are you willing to pay a premium for his tactics rules, and take the survival gear as a bonus? Do you find his rules "game changing", "helpful", or "Meh..." ?
I take Zahndrekh for neither of these reasons- I have him because I like his background! I dislike playing 'evil' armies and the Necrons generally come across as 'neutral' really which is a bonus for me, but Zahndrekh is even better as he is an honourable general. I like his vibe and his eccentricities.
His background is also the reason for several unit choices- I restrict myself to not using 'dishonourable' or assassin type units- so no deathmarks, wraiths, destroyers etc. While Triarchs fit in well with this themes' ethos.
His abilities are helpful mostly and sometimes game changing.
Question 2: How long do your fliers last? With the two mediocre armoured fliers, do you face enough Anti-flier to worry you, or do they tend to survive long enough, or 'till the end of the game?
They tend to survive most of the game, if not to the end generally. Cunning use of scenery to give cover saves help plus giving the enemy other things to worry about. Really, if you look at it- an Annihilation barge can do more damage and is easier to kill, so the Nightsyches become a lesser threat. Also, it's never a bad thing to have them fly off the board sometimes- if you can't get any worthwhile shots in, just zoom off, stay safe for a turn and come back in a better position later.
Question 3: Do you take Gauss cannons on the AB's because you find they're more useful vs MEQ targets, and the bonus strength isn't that meaningful when you can still glance vehicles on 6's?
I take Gauss cannons on the Barges because while making my first one, I accidently assembled the wrong gun. I like my units to follow a certain symmetry so thought 'sod it' and built the rest like it too
They are useful though- having that odd shot at Ap3 is good for blasting marines. Mostly they're always snap shotting though as I'm moving aggressively towards my foe.
Question 4: I've looked at Triarch Stalkers before, and wasn't sure if they'd be "worth the points". Seeing as how you came in 3rd, I'm guessing that they are. 
Do you think they'd be as successful in a list with less AV 13 units? Do you tend to spread their shots around, to twin link multiple units, or do you tend to focus on a target to ensure it's destruction? Are they good as "one of's" in a list, or do you need to use multiples to see their greatest effect?
They look cool. This is what makes them worth the points
Seriously, they're big freaking insect things that clamber over terrain and blast stuff- so cool!
I will spread their shots around to make better use of the targetting ability generally. The focus fire comes from the Immortals as they blast up a targetted unit until it's dead and then move onto the next one. Having a 2nd unit targetted is useful for when you've disposed of the first threat.
Having them as a single one-off unit is fine as long as you have other armour for your enemy to shoot at. It's the same in any list- take a single nasty vehicle and watch it die in turn one.
Having lots of AV13 helps for sure.
Question 5: Are you able to usually avoid close combat in a game [with your Immortals, in particular] or is it something that you have to deal with on a regular basis?
I can play games where there is little combat definitely- overwatching tesla and heat rays are very nasty. I will often use the Stalkers as tar pits to save an Immortal squad from combat. If combat is definitely going to occur then Zahndrek giving furious charge or counter attack to a friendly unit is very useful, as is removing those abilities from an enemy.
Generally though, I can use the vehicles to screen my Immortals to stop them getting assaulted.
Question 6: Do you use Zahndrekh as a tank for his Immortal squad, and LO,S! wounds that could potentially kill him?
Not really- Zahndrekh is an exalted general and tactitican- any Immortal would be honoured to sacrifice it's life for him!
I try and play 'in character' and so don't use characters to tank enemy shooting- it doesn't seem realistic and is a naff way of playing imo.
I hope that helps- though I realise there's not a lot of tactics or strategy involved in my answers!
