Hmmm... I'd recommend the strategy primer on
http://www.bdominia.com about this one.
21 land with a blue deck is hardly enough, since decks can run 24-28 because it's really needed. If you don't have Thawing Glaciers, especially, you need more land.
About the first question, if you don't have Powder Keg or any sort of early defense (even Quicksand or Mishra's Factory to block or anything) I'd really recommend the walls as the cheapest alternative.
Your counterspell base also leaves a whole lot to be desired. You can use 4 each of the common cheap counters like Mana Leak and Counterspell before having to go to higher, awkward counters like Rewind.
You should also pick up Impulse, which is a common. Brainstorm is useless in this deck since it has no Thawing Glaciers to reshuffle the top of the library away, and it's useful only against discard decks to hide cards.
Memory Lapse is useless here since the deck can't use the extra turn to rush the opponent or anything. And so on.
I'm not quite sure what Mind Bomb is supposed to do, but it can be replaced.
All the Unsummon spells don't have much of a point since they don't really kill anything. If you want this, you could use Capsize, another common, but there's not much of a point, either. Something like Waterfront Bouncer might be more fun, and that's another common.
As for the creatures, do you want little blue flyers and some pingers? I think Stinging Barrier and Suq'Ata Firewalker are the best pingers available to you here. Supplement these with Wall of Air and maybe Fog Bank, as I think these are the best flying walls you'll have, then remove everything else for a big uncommon flyer like Air Elemental (the ideal one is Morphling, though).
You'll still need a number of utility cards against funnier stuff like shadow creatures. One good non-rare that will fit right into your deck is Dominate. Bribery is useless in this deck since for the cost and rarity, you can just play a Morphling rather than a creature your opponent might not draw. Go play Treachery if you want a rare that costs a lot of mana, at least it'll take away a creature that's already on the board (opponent loses 1 creature, you gain 1... net gain of 2).
Card drawing is yet another, and if you can't get your hands on Ophidians, Whispers of the Muse from Tempest should do well in casual play.
I saw the Archivist, but he's a 1/1 that's rather easy to kill.
Adding something like Hermetic Study isn't very useful since for one more mana you can just play a real pinger, and you don't have that many creatures here.
Have fun!
