Well, it's not a bad start, but yeah there are some things I'd change. First, I'd ask whether you have
Sower of Temptation unlocked (it's the reward for one of the later challenges) so it might be unusable for you, unless you did that one already, and I would find that surprising since the Gimme! challenge is much harder than this one, and not one I'd recommend starting with.
If I were to build an affinity deck like this, I would remove both the
Darksteel Colossus and add one
Blightsteel Colossus. (it's a new card that is much better) You don't need two because you will never ever cast it unless you get
Tinker, or maybe
Tolarian Academy + enough stuff that you've already won.
Also...
Tinker is restricted so if that deck works, then Jatill has to change that :p If it is working for you, milk it for all it's worth! Anyway, to make the deck legal I would also take out 3
Tinker.
I would also remove both of the
Sword of Feast and Famine, because untapping your lands doesn't really help that much in this deck. I probably wouldn't use any equipment (more personal style than anything else) but if you are dead set on it, I'd probably pick
Sword of Fire and Ice instead, because card draw + killing weenies (or +2 more damage) is better in this deck than opponent discarding + you untap lands. (plus protection red is handy against some of the red decks)
I would also remove
Akroma's Memorial because you won't get to cast it very often. I can see why you are using
Unsummon, but
Echoing Truth might be a better choice. It's a turn slower (which can be a problem, given the AI is starting with a creature on turn 0) but it unsummons all copies of the card.
I would also exchange the qumulox for more frogmite/myr enforcer/master of etherium, because those are quicker.
I haven't counted how many cards that this all changes, but I would also do my best to cut the deck down to 60 cards if it isn't already. I usually run a 60 card deck with 23 land, unless it has an abnormally high number of very cheap or very expensive spells. (most people these days seem to use 24-25 or sometimes even a bit more, but in my day it was usually 23)
If you want some spoilers, my thread here talks about the challenges:
viewtopic.php?f=57&t=3790 It covers about 3/4 of the challenges, and has all of the challenge quirks and and at some point I'll get around to redoing the rest.]
edit: looks like you took some of the suggestions before I even posted them :p