1. Not exactly, it's better to work forward rather than working backwards by subtraction.
Acquisition debt is debt used to buy, build or substantially improve your home. Suppose you bought a house for $180,000 with $30,000 down and a $150,000 mortgage. Your acquisition debt is $150,000. Sometime later you refinance for $180,000, and the original mortgage has been paid down to $135,000. Your acquisition debt is now $135,000 and that carries over to the new loan. If you then use $20,000 of the proceeds for an improvement, your acquisition debt would then be $155,000. You can include some of the closing costs, but not all of them, in the acquisition debt. See page 8 here.https://www.irs.gov/pub/irs-pdf/p523.pdf
2. The improvements must have been completed 90 days or less before the refinance, up to 2 years after the refinance. But they don't qualify as acquisition costs until you actually pay for the improvement, you can't deduct the interest now based on your future plans.
