I really like your deck, I would definitely say a fusion gate or two wouldn't hurt and also you should try and take out 1 copy of gierfried and 1 darkstorm for them. I have been experimenting with gemini myself, and I think I will attempt a list similar to yours.
Gemini Booster would be amazing for this. A 700 atk booster is awesome, plus if it is destroyed, u can make a Gemini monster gain its effect without normal summoning it.This works wonderfully with Dark Storm Dragon since it allows u to get rid of those pesky Mirror Walls Enemy Controllers and OTC.