Summarizing, in order to owe an underpayment penalty, you and your spouse must have
1. total federal income tax owed must have been $1k+ what you paid/withheld
2. paid less than 90% of what you owed
3. paid less than 100% of what you owed in 216 (110% for high income, defined as $150k for 2017, not sure what 2016 number was, probably the same)
I personally aim to hit number #2 every year, and periodically update a spreadsheet which ballparks our expected federal income tax.
You mention losing your spouse's income for this year, so it's probably not in your best interest to aim for #3 as you will likely overpay, maybe by a lot. I'm only in total market mutual funds, so I estimate dividends by assuming 2% of my taxable accounts, your math may be more complex if you hold individual stocks/bonds. Plug that into some tax estimator along with your expected pay, work deductions, etc. (I use a google sheets doc of my own making,
Taxcaster is not a bad place to start if you want a quick and dirty estimate), figure out what you should owe, and aim to hit it or go a little over, and you should have no problems.