Your company's HR department may have info available about the tax consequences of your stock options, but perhaps you could reduce taxes by watching the timing of exercise if your household income varied from year to year.
i.e. if your income was regularly under the Social Security wage limit of $127,200, then it might make sense to exercise multiple options in one year to get above the SS wage limit and avoid 6.2% tax on the amount over the limit. Of course, the opposite could also be true, where it might make sense to only exercise a few at a time to keep your income in lower federal tax brackets. Would be best to consult a CPA who understands your entire household income picture.
Also, the tax implications for getting a cash out refi or HELOC are in regards to the mortgage interest. Your home mortgage interest is deductible on 1040 Schedule A only if you itemize, and interest on a rental property mortgage is deductible on Schedule E, taken against the rental income regardless whether you itemize or not. If you take a cash out refinance, then this interest will be deductible on Schedule A only if you itemize. However, if you take out a HELOC and use the proceeds to purchase rental property, you can deduct the interest from the rental income on Schedule E. The second way is likely to be slightly better tax treatment, but your CPA can look at your overall picture and let you know which way is best.