This may sound cold hearted, but It hasn't been addressed by anyone yet.
What is her life expectancy now? How many quality, active years are expected?
I think both need to be factored in.
If she only has 4 or 5 years expected, go for it now. If more, wait a while, 1 or 2 years. When she's gone, you probably can still work. Your expenses for one will be less than for 2. $4000/month seems adequate.
It also depends what your immediate plans are. If you want to take an around the world trip now, that will certainly deplete your savings. Maybe that needs to be re-thought? Just an opinion.