Problems with changing valve covers?

I just changed the valve covers on my 1957 ford 312 v8. They are the same valve covers and gaskets, they just needed to be replaced due to rust, age, etc. I did use gasket sealant but I am not sure what kind it is. I found a tube of it in the garage and the front was covered with grease and unreadable. I could however read on the back the instructions that said to use it for gaskets, covers, etc. It smelled a little like a crayon, was black and a little thicker than grease if that helps any, and i put a good layer on each side of the gaskets. I was not sure how tight the nuts should be so I just tightened them until the rubber washers started to compress and squeeze out a little. I just want to make sure that there is nothing that needs to be done before i start the motor. And if I did do something wrong, what problems should I look for?