Around $32,600 of discount/spread in exercised ISOs would give you a roughly equivalent total tax between the regular and AMT systems.
With these numbers, under the regular tax system you'd pay $22,679 in federal income tax. Your tentative minimum tax (TMT) would be $22,672. If your ISO spread went up to $32,700, your TMT would go up to $22,698, and since it is larger than the regular tax, you'd pay the excess $19 of AMT.
I put together a spreadsheet to do this calculation (https://docs.google.com/spreadsheets/d/1m3Ss4yO46Z4Jno0nqQirSIcSw72ADfS-5EkKVudCYXs/edit?usp=sharing; note that it assumes your AMT income is <= $1,000,000 such that the AMT exemption is not phased out at all) but it can be a bit of a pain. You're probably better off putting data into TurboTax or similar software. I did this as well to confirm my numbers.
And yes, as you note, if you pay AMT due to exercising ISOs, in future years you can receive a credit for the extra tax you paid, limited to the excess of your regular tax versus TMT in that year. Unused credit carries forward into the future indefinitely.