I'm sorry for your loss.
I inherited an IRA from my dad a few years ago. It wasn't enough to retire on - but it's enough that I'm very close... moved my retirement up by a few years for sure. In the meantime I take the RMD to pay down my mortgage and fund the kids 529's a little more aggressively. This helps me save more $$$ towards my retirement nest egg.
I'd definitely run things through firecalc. Also - you need to know your spending. That's probably the biggest thing you need to know. When you input your spending in Firecalc - that's the gross... so you need to your budget to include the taxes you'll be taking on the inherited IRA's distributions. Make sure you explore all the tabs in firecalc... So you can input any social security and/or pension income.