DedWards

I see you put Brave the Elements in the sideboard, but I think it works better in the main. Besides the obvious defensive use, it can also be used to make all your creatures nigh impossible to block as most player's creatures normally share 1 common colour :p Also you can use it to mass block and have your creatures live. Versatility is key XP

Suppression Field has given me an idea for an anti-creatures deck. If I'm correct, Magus of the Tabernacle + Suppression Field should make each creature cost {3} to keep around (sadly this includes the Magus too). What you think of the idea?

Wouldn't Elspeth, Sun's Champion or Elspeth Tirel fit the theme better than Elspeth, Knight-Errant. The other versions put out 3 soldiers at once, thus gaining you 3 life per 'Soul Sister'. Ajani, Caller of the Pride's -8 could work with that too...

I just realised that Teleportal would be a cool card in here, even if it's just as a sideboard option.

I've been wanting to use Locket of Yesterdays in a similar deck myself, how's it work for you? I've found it to be a little slow, and thus been trying to rather work it into a storm deck.

You seem to be lacking in turn one plays. Disenchant and Righteousness are your only 1 mana spells and Righteousness requires you to have a creature out. Mite I suggest moving Disenchant to the sideboard (it's a situational card) and instead adding a 1 mana creature? Student of Warfare is an awesome 1 mana Knight.

I see that you are also 4 cards short of the 60 minimum, Mite I suggest four of one of the following to fill that gap:
Leonin Skyhunter
Spectral Rider
Mirran Crusader
Their combat evasion (especially Mirran Crusader) makes for awesome offensive plays.

Another type of card you may want to consider is some form of removal. The best mono white creature hate in Modern is Path to Exile.

The Goat Overlord is pleased. As her advisor/messanger, I am obligated to point out that Scapegoat, though flavourful, is the only card preventing this from being a Modern legal deck. A good replacement that'll get some Goats out of Springjack Shepherd is Cloudshift.

Silhana Ledgewalker would be a good creature to attack Spellbinder to.

The Ready side of Ready//Willing and Rootborn Defenses are two very nice ways to 'counter' a board whipe. (I prefer Ready myself)

no. Relentless Rats only breaks the 4 copy rule

Ratcatcher, tough a little pricy, mite fit in here?

Also, Swarmyard would work nicely in here

I've seen Beastmaster Ascension make attacking Saprolings a force to be reckoned with.

Door of Destinies, Coat of Arms and / or Gaea's Anthem could work nicely in here.

3 life per card revealed, I've yet to find a better once off healing effect, especially along side creatures that get better the more Life you have.

I've played them a few times in my elf token deck. They're nice, but I found the spot wasted and replaced them with more copies of Ezuri.

Amulet is also a good sideboard option against decks that are heavy on creature removal.

Experience with my Double strike deck has taught me that creatures with just double strike at 3 mana (ie Hearthfire Hobgoblin) cost too much. It's better when they have at least one more ability attached, like Mirran Crusader. 2 mana double strike is ok.

Designed a deck on double strike. Mite give you some ideas:
http://www.mtgvault.com/dedwards/decks/double-double-strike/

I've always wanted to use Sadistic Sacrament in a mill deck that says stuff like mill until he reveals X lands. The {B}{B}{B} in it's cost may be heavy, but with the correct dual lands, at least 3 Sadistic Sacrament should be ok.

Also Surgical Extraction and Extirpate can target non basic lands in graveyards. This would provide a similar, more reliable role than Sadistic Sacrament.

I'd drop Archangel of Thune by one, Felidar Sovereign by two to add three Martyr of Sands. They are mana HEAVY and the Martyr will buy you more than enough time to get to them. I've played against a few lifegain decks and majority of my losses are because of the life gained off of Martyr

One or two Quicksilver Amulet could be a nice backup to the Piper