You have a good start here, but at the moment your creatures don't really help your overall objective.
First off, are you worried about maintaining a specific format? At current it says your deck qualifies as "Extended." That's ultimately going to decide which cards you're going to keep or need to pick up.
One creature that the best mill decks just NEED is Hedron Crab. Every time you play a land, they lose three cards. Play one on the first turn and another on the second turn and you've already cost them three cards and on turn three when you play a land, BAM, that's nine total cards down already. Also, they're good blockers for early game.
For other creatures, Fog Bank and Guard Gomazoa give you incredible blockers that can stop practically anything without getting killed. The only real problem you would have there is with trample damage.
Thought Scour and Mind Sculpt are GREAT. But you should also pick up Traumatize, Increasing Confusion, and Jace's Erasure. Each of those will give you more spells that can drop a LOT of cards quickly.
Another fun card to work with in a Mill context is Geralf's Mindcrusher which can serve as a big creature if you get stuck trying to win with damage, OR, you can pair it with Nephalia Smuggler/Deadeye Navigator/Ghostly Flicker/Conjurer's Closet to flicker and repeat the ETB effect, causing your opponent to drop cards five at a time. If you have Altar of Dementia you could make them drop another 10 cards when you sack it and then just flicker it to lose the undying counter - rinse repeat.
Trepanation Blade is a good piece to pair with any creature as it normally will cost them 3-4 cards per attack, if not more. Keening Stone can be a good win condition as it can snowball VERY quickly.
I would also recommend consolidating your countermagic as it's really scattered at the moment. More Mana Leaks, Unsummons (or even Boomerang). If you're open to any format, Temporal Adept is a great option that can essentially give you as many Boomerangs as you could want.
Lastly, Jace, Memory Adept is perfect for mill decks. His +0 ability results in an opponent dropping 10 cards. If you can protect him at all, that can REALLY add up quickly.
I hope all of that helps make sense. The best part being not much I've suggested is all that expensive. Jace is pretty pricey (~$10) and Altar of Dementia is mid-range (~$3-5), but outside of those, pretty much any of these should be around a dollar or less to pick up.
Good luck!