Looks yummie!!!
Well, for the cake pan, yes...you should dust it as lightly as possible and tap out all the excess. Otherwise you can get those white little globs of stuff on your cake sides.
As for the frosting....I've NEVER heard of using evaporated milk in a frosting before. Thats why it came out runny. I would have left it out. If you want to add a dairy ingredient besides butter, then think you could put a pat or two more of butter in there, or a couple tablespoons of dried milk, or even a tablespoon of heavy cream.
If you ever get runny frosting, you can use some of my tips in my other posts.
I love heavy chocolate tasting frosting. I would have put more cocoa powder in the mix instead of sugar and then whipped it on high, in the mixer.
It might have also gotten runny because it was too hot. You do want to use room temperature ingredients when making the frosting, but once you cream the butter with the salt, vanilla, and any other wet ingredients you might have....mix it well with one cup of the sifted confectioners sugar, then put it in the fridge for 5 minutes, so it can cool down. Then you can start mixing in the rest of the sugar. You can always stop and let the frosting rest in the fridge for a few minutes if it gets hot again.
And by "hot" I mean, the frosting gets really loose and runny. If the cooling down in the fridge does not work, then it definitely needs some more dry ingredients to firm it up.
In this case you can use more sugar, which you did. Or you can use more cocoa powder. You can use flour, if you know how to use it in a frosting, otherwise it tastes horrible. You can also use a little bit of dry gelatin in the mix, or dry packaged pudding powder. Some people even use a little bit of cornstarch.
