I do pretty well year round - In fact, January is actually one of my best months. I primarily sell on eBay, although I do put a few things on Etsy as well. I also accept a couple of commissions each month, and do one big show a year (the Ghoultide Gathering, up in Michigan). It does take a while to build a collector base on eBay, but the market is definitely there year 'round. The trick is to do something new - something no one else is selling there. At the time I started there were very few Halloween artists. Now there are scores of them - but many just copy what others are doing, so never really make much of a success of it....It takes time and patience (the first couple of years I had to let a lot of pieces go at a loss) but if you find a niche, there's definitely a year-round market.
Not sure if this will help, but a couple of years ago I was getting quite a few emails from people inquiring how to get started selling art on eBay, and rather than write it out each time, I wrote one of those eBay "guides"....if you're interested you can look me up on eBay under the seller name kingofmicestudios, click on my name, and there should be a link there to the guide.
The digital idea incorporating painting sounds interesting, and seems like it would hold lots of possibilities - prints and notecards, Book of Spells pages, etc...