And be sure the accountant knows what he's talking to. I did that and it was still fail, because they didn't understand ISO+AMT Tax Trap.
As someone who's lived through this, immediately (as in the same hour you purchase the ISOs) sell the ISOs. All of them. Take the short-term capital gains hit. The alternative can and will destroy you.
Going for long term capital gains will only destroy you if the stock falls, which can happen in any investment.
If there is enough confidence in the stock, a happy medium can be to sell enough ISO's at the time of exercise to cover the tax cost for that year. However, if the stocks you have are a massive % of your overall (potential) wealth, short term tax on a big # is still better than long term gains on a volatile #.
As someone who's lived through this, immediately (as in the same hour you purchase the ISOs) sell the ISOs. All of them. Take the short-term capital gains hit. The alternative can and will destroy you.