I would use at least 4 SoGs and 2 sancs for healing, although the sundials might help reduce need for heal..but imo 3 SoGs isnt enough healing to keep u alive :O
I find it's usually more than enough. There's also a Jade Staff.
You don't actually get hit too much, I usually stall with some sundials if I need to until I can get bonewall up and start spamming pandas/RoF/UGs.
By then you should have enough counters and CC to keep damage at bay until you can win. You can also use sundials to stall a couple turns if your bonewall is low until you can get back more counters.
There's really 3 auto-quit situations:
1) BH/Gravity Nymph
You just can't get set up fast enough. you might stand a bit of a chance with Sanc in the picture, but even then.
2) Pulverizer/Heavy PC
With so much reliance on permanents to mitigate and deal damage, extreme PC can Cripple the deck.
Hermes or DG with their neverending explosions just denies you any chance of a decent set-up.
Obliterator on the other hand will just destroy all you gases unless you get 2 nymphs out, making it difficult to get your damage going.
3) Reflective shield. Self explanatory. You stand a chance if you use pandas to try and TU your opponent's heavy hitter, but otherwise you're usually left with no chance.
If you see Thorn Carapace, Fire Shield, or any other harmful shield, it's a good idea to use sundials to keep your nymphs from getting hurt. Otherwise quint generally keeps them safe.
Alternatively, you can add a pulvy, but I don't want to make the deck too bulky.