It can be remarkably easy to get the Artist Visa (I have one, it was approved about a month ago).
I think variable factors that could make this more difficult may be:
*your country of nationality (sadly this seems to be of importance for how smoothly things go for you, I am from New Zealand, which is one of about 6 countries that Germany privileges)
*your ethnicity (likewise, I think this sadly can be a factor, I am white, but a friend here from Nicaragua has a much harder time from officials - and he has Italian residency so he's technically allowed here with almost no questions)
*whether you have good German language skills or can bring someone along who does (my partner is German, so again this was easy for me)
*and the general mood of your immigration officer at the Auslaenderbehoerder. You are allocated one officer based on the first letter of your last name, so you never have a chance to switch to a new official.
Things you might have to do (but which I did NOT):
*prove that you can support yourself (bank account or similar statement proving that you have a minimum of 800 euro available each month for the next year)
*or prove that your art is profitable and provide a business plan. Again I did not have to do this.
Other things I did which my officer was not even interested in seeing (but yours might be):
*provide an artist's profile including my training, exhibition history (yours may vary), and examples of work. They simply flicked through mine and handed it back to me.
*a certificate from the police in my country, saying that I have no criminal record. Again, they never even wanted to see this.
*my partner is working, so he was prepared to sign a statement saying that in case of financial trouble, he was willing to support me, but they never wanted to see this.
The artist's visa is a freelance visa. That means that you have to pay your own tax etc, you'll be self-employed.
The reason the visa can take longer is because your application won't be approved by the Auslaenderbehoerder, they will forward your application to the IDK (the art and conservation institute or some such). Mine only took a couple of weeks to come back, plus another 2 weeks for them to have my Ausweis ready.
I applied for another condition on my visa: English language instructor (since I had an offer of work through a language school). There was an offhand comment from my immigration officer that the artist's visa is *easier* to get than the language instructor visa (and I had a letter from the language school saying they needed English native speakers, there would realistically be no way that this would have been declined).
Regarding insurance: there is a state subsidised insurance for artists, but I think you have to have worked in the industry for a few months before you can be eligible to apply for it. That means that you'll need to get other insurance just to apply for the visa. It's a bummer but that's how the cookie crumbles.
Good luck.