The best way to find out if that's a good idea is to use the Marketplace Insights tool. After entering Instructor mode in Udemy, you'll find it under the Tools menu. From there, you can explore lots of interesting stats around the "Handwriting" topic.
The short answer is that there is a fair amount of demand for courses on handwriting, and the median monthly revenue for courses in this area is $53 / month. If that sounds worthwhile to you, then go for it! The most successful course in handwriting earns $338 / month, so that's pretty much the upper bound.
The top-earning course in this category is only 3.5 hours long with a 4.4 rating; so if you were to make something both better and more comprehensive, you'd have a shot at displacing it. But for your first course, the median revenue is a more realistic expectation.
