As for your deck the way it's constructed....
purphous strikes me as an unusual choice. You've got very few creatures to come in and activate him and his mana sink isn't useful the following few turns after he comes down. He's only valid late game with elspeth or assemble, and in the case of assemble it's very late game. I feel it's "win more" assemble and elspeth are must answer cards that become inevitable win conditions the longer they're on the board. Deal with them or die. Purphous accelerates that, but doesn't really add anything.
Go down a land or 2 and get you some more "stuff", you're topping out at 6 with no X spells to dump mana into, 25 land should be more than enough to get there. Control decks usually only run 26 maybe 27 lands, if you're worried about flooding or being mana starved get some more scry in the deck with magmajet or temples of silence.
Frostburn weird is also a no go for me in this list, while it stone walls aggro you're already doing that with a removal suite and cards like reckoner. You don't need a 1/4 wall that "might" trade with an attacker/blocker. The reason it works in mono blue is because thassa can make him unblockable and pump him at the same time with nykthos.
I really want to see something like fiendslayer paladin along with an anthem affect like the spear. a 4/4 reckoner and a 3/3 first strike liflink jedi is pretty good. That turns on heliod when he comes down and also gets you some more cushion so you don't get burnt/aggroed out early game. The burn deck is a real thing man it top 16'd the GP this weekend.
Anger kills all your dudes... and invalidates your whole strategy, move those to the side at least if not outright cutting them, you're already setup pretty good against aggro.
My final opinion... i can't endorse the deck as constructed...
The deck has good cards in it, but if you go this route then the RBW midrange has a better cards available to it (blood baron, obzedat) as well as a better emoval suite. Or it seemed like you had the cards for the UWR control deck which is a good deck and has the ability to shut off lots of stuff. If you have sphinx's, spheres, and verdicts aren't hard to get a hold of, i don't understand the aversion to trying something more proven and go with a UW or UWR build.
You've got conflicting ideas here, midrange, devotion, white... white devotion is an aggro deck because that's the way wizards constructed it. The white devotion plan really needs to be an aggro one. Soldier of the Pantheon plus something like dryad militant, precinct captain on turn 2, or possibly a wojek halberdiers, skyjaks or something, turn 3 ajani, reckoner or spear and you're talking some serious damage on the board. THen heliod to top it off. It can go "big" with stuff like archangel of thune and gideon, but you need to be beating things down with creatures, gaining life to survive. A midrange deck typically runs the best removal available and frankly right now that's in black.
These midrange boros decks were all theorized and tested early in theros release and they really went no where. They ended up evolving into WR aggro, White weenie decks and just RDW/red devotion. The Dega midrange is all but gone and that basically evolved into the RWb burn deck that's floating around or a BW midrange, and if you're not completely married to the devotion plan, the RWb burn deck works. It can beat mono black and all the other contenders out there right now.
I realize like you said that your store isn't hyper competitive, but i think you can build a solid tier 1 deck with what you have represented and there's no real reason you shouldn't go for it.