My initial thoughts are that Storm Herd is never going to work in this deck. You're just not going to be able to get it into play as you'll have either won or lost by the time you have 10 mana available. How about Sacred Mesa
If you're running Prized Unicorn, then you definitely want some way to give it deathtouch - if not Basilisk Collar, then something else - otherwise it's just not worth playing his four-mana casting cost.
I'm not convinced by Armored Ascension - it seems like more of a mono-white card to me.
may be worth thinking about in place of Thundermare, as not only can it see itself onto the battlefield earlier, it eliminates your need to run red in your deck. A two colour mana-base is much easier to organise than a three colour one.
You may also find some useful stuff if you do a text search for 'Horsemanship' on Gatherer - it's always handy for making your creatures unblockable.
Hope that helps!