The DTI are pretty set in stone as far as I know - our LO said they were strict about it, with no real wiggle room. Though they will give you the chance to get your DTI to where it needs to be by paying down some debt if you can.
The FHA rates I saw today are about 4.75% - I don't think you can get USDA rates online, but your lender can tell you the current rates, and they should be similar. They are going up, daily it seems.
Just to be aware - some states are starting to run out of USDA funds for the year, and as well as that the USDA map is supposed to be changing Oct 1st. It might get delayed again, as it was back in March - but it looks like a lot of areas that were USDA eligible will no longer be in the very near future, or the near future. The house that we are buying will no longer be eligible when it goes through.
Our closing costs are about $5,000 - we've already paid $500 earnest money and $400 for the appraisal, so those will be credited back. And we opted out of owners title insurance so there will be another $900 credited back. We paid $400 for the home inspection, but that is optional and paid out of pocket. The total seller concessions for us are $2500, plus there is another $2500 we can add to closing costs due to being able to finance 102% of the appraisal price to cover the USDA fee. Our purchase price is $124,000, but the appraisal came in at $126,500 and so the total we can borrow is $129,000.
We thought we would be bringing very little to closing, and the committment letter cited something like $0.60. HOWEVER, the taxes come due here in September and there was a sudden increase - and these are prepaids which have to be paid at closing but are classed as a separate thing from closing costs. Plus there is the USDA fee of $2000 which is factored in too. We were told just a week or so ago that our TOTAL - closing, plus USDA, plus prepaids was $12,000, and that we had to show $6500 in our bank account to cover what it would be after credits. 
NY has really high taxes and closing costs, though - I'm sure yours will not be like this!