I know nothing about inserts.

I know abut woodstoves. I know the best woodstoves those purchased to address the size of the room/rooms they are expected to heat. The huge ones in small spaces are too often frustrating to operate, leave you unbearably uncomfortable, and frustrated. Bigger isn't necessarily better!

I think you should think about the age and insulation of your home... and use that as your guideline in determining what you will need to keep your home at a comfortable temperature WHEN YOU'RE THERE. Let's face it... if you're working, do you really care if your home is 55-60 degrees? You want to come home, feed the whatever, and have it come up to nice comfy temp. while you're "hanging out".

An insert is really just a woodstove that has some variations for placing it into the fireplace opening, that's all.
But I think you've got to find out what kind of fireplaces you have. Masonry or zero clearance prefab? Then talk to your stove shop about what they have to go into the unit. Some inserts are not rated for ZC installations, so make sure of what you have.

When I lived in PA we too had electric heat and we put an insert into one of our fireplaces. And loved every minute it was going! It heated the house quite nicely to a point where we shut off the electric heat completely in the main living area and never turned it on for 10 years!

But also look into the availability of firewood in your area. Do a comparison between cordwood and pellets.

Personally, I don't like the fire from a pellet stove as it's too "busy" for my tastes. And if you go the pellet route, make sure you get a battery backup for when the power goes out. That's one nice thing about wood. You don't need power to keep warm.