Something - yes. Something which implements everything required and is tested - not likely.
There's a huge difference between converting data from your little hobby and converting the vital knowledge of your company. It's different because it's more mission critical - you don't want to screw it up.
It's also different because the bigger dataset is likely to have some customizations and other "small" stuff which tends to matter in big perspective. You might be okay for losing e.g. votes if it's a small data set, but you really want it in with a big one.
Sorry, that's nonsense. Each one of the systems is going to have a different schema and constraints for users, posts, comments, votes, that most likely will not have a one-to-one mapping.
depends on the system - 30 minutes is not enough to convert users, groups, permissions, threaded conversations, voting, keywords, etc, especially if both systems do not use the same data model.
Or you can write your own converter - it probably takes ~30m to whip up something in Python.