Cowboy custom bikes is best suited for short city runs and weekend rides on the twisties. The occasional highway rides are also fun but the wind blast at high speeds will soon tire you. Extra adons like a windscreen might be available and can help this. However only opt for this as your highway bike if you can live with the rev happy nature and harsh sounding engine.
We all make mistakes but during a motorcycle build you want to avoid making them if possible. For example, when you are building a cowboy custom bikes you have an idea of how the project should go, what you want the bike to look like, the budget you set for it and so forth. As you put together your list of what you need, a time frame and budget for the build and everything else you may leave out a few important things.