Lizardmen are unique in that we are the only army that is allowed to make the Slann the general and the BSB. It's usually advantageous to do this. I would advise putting all your eggs in one basket. Your Slann is your primary caster, your general, and your biggest single points unit. It's very little consolation if you lose a Slann but you have a Saurus BSB still alive.
More likely your Saurus BSB will get picked off individually and then your Temple Guard will fail a break test. Temple Guard with a Slann general and BSB are going to pass 100% of their break tests, especially if you involve the Standard of Discipline (which is nice and cheap and raises your Slann/general's Ld to 10). That's something I personally take for granted.
I believe for Lizardmen armies with Slann you want to put all your eggs in one basket and fortify your basket with everything you have.
2 Skink Priests, one with cloak of feathers to get where I need to be for missles/direct damage spells
Cloak of feather is nice, but it's a luxury. I would rather use those points for more Temple Guard. A Skink priest in a unit of Skirmishers has a 12 inch march move and can move in any direction. That's almost as good as a cloak of feathers.
and the other with egg of quango to (hopefully) give the inevitable DP or Chaos Knights a nasty surprise when they charge thinking to get a quick kill.
Hypothetically lets say your Skink priest and his Skirmisher units gets charged by a group of Chaos knights and then you roll a 4+ with the Egg of Quango and when you score 2d6 Strength 5 hits you roll 12 hits, huzzah.
12 hits, 2/3 of them wound. That's 8. Chaos knights have a 1+ save which becomes a 3+ save. That means you are only going to kill 2 or 3 knights under ideal circumstances. The Skinks will be butchered liked sheep and the Knights have +1 CR for charging and +1 for a standard. Despite losing a couple men, the knights are almost certainly going to break and run down the Skinks, Egg or no Egg, even if you rolling 6s like it's going out of style.
Generally speaking, the Egg of Quango is for offense, not defense. The Egg of Quango might be a nice surprise for a Slann to carry or even a Saurus OB. But the traditional use for the Egg of Quango is to give it to a Skink chief on a Terradon or Ripper.
You'd be better off using the points for Temple Guard.
SV BSB with Razor Banner and SV with GW and Armour of Destiny
That is against rules. Except for Slann, it is illegal for any BSB with a magic banner to have any magical items, so IF you run with a Saurus BSB then either Razor Banner has to go or the Armor of Destiny has to go. Personally, I think it's a bad rule and I wouldn't mind house ruling that BSBs of all stripes can bear magical banners and magical items, but if you want to play the RAW, you should drop the Razor Banner because a BSB with a magic banner and no magical defenses is basically a pile of free victory points for your opponent.
My advice is to definitely give the BSB to the Slann. You
might want to consider dropping the Scar Veteran altogether. You probably want to give him a great weapon and tool him up for offense. If a character is not a BSB, general, or spell-caster, an opponent is unlikely to bother allocating attacks against said character, at least in my experience. In most cases, I can get away with Scar Veterans packing great weapons and possessing no defensive magical items at all because the enemy always tries to kill rank and file Saurus Warriors instead.
Or perhaps, give the Egg of Quango to your Scar Veteran. Then your Saurus Warriors will have comparable killing power to the Temple Guard for one round at least.
2 Ancient Stegadons with EotG for 6+ save (one for each infantry block as above for their own 6+ ward, impact hits and thunderstomp)
I was going to say that you don't need to do this because your Saurus have a parry save but then I noticed you gave them spears. That's how rarely I use spears on my Saurus, I forget it's an option. This double EOTG Steggies is a good choice here.
If you are really desperate for more TG bodies, you could drop the EOTG. If you do, you probably want to give the Saurus Warriors swords and board and you probably want to give the Slann the Iron Curse Icon to defend your TG against the Hellcannon. In fact you might want to do that anyway just in case the TG get hit by a Hellcannon after the Steggies are dead. Iron Curse Icons are only 5 points.
I could cut out one unit of Skink Skirmishers and add some TG...
It's hard to have too many Skink Skirmishers, but 40 is probably plenty. You don't need 50. Especially since Chaos Warriors are hard to shoot at with Skinks.