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I am no expert but you should have no problems getting approved
Credit history will be fine.
Debt to income ratio should be fine too.
If you can get your scores up to the 700's then I'd recomment conventional financing over FHA. Conventional will require a 5% down payment, and you also have to consider closing costs too (you can always ask the seller to help you out with closing costs).
Other than having to explain what the inquiries were for, and if any new debt resulted in them, then inquiries have minimal impact other than what they do to your credit score.
I think your plan should work out.
Often credit unions offer very low ARM rates. I am not sure who is offering the lowest though.
Your credit history and other details look fine and I don't see anything that might cause trouble in your mortgage plans.