I bought a used Nikon D3100 with a shutter count of 551. Is that good?

Is there anything else I need to consider?

I guess it depends greatly on what you are trying to accomplish with it.

Just like new…

That's very low. You can take another 150, 000 photos with it.

Thats pretty much a brand new camera. A spare battery would be a good investment.

That's very good, the shutter count for Nikon d3100 is about 150, 000