Can you do subscription if you have downloadable content?

You can create any model you like, whether people pay is another question.

The subscription model is the holy grail, though psychologically it is also a much harder sell that people don't often take into consideration.

So, of course it would be much better financially to have a subscription, there are many companies that offer membership (monthly/yearly) for access to benefits (events/content/etc).

I don't really know about your audience, but if it were me I would have a look around and see if people in your space offer subscriptions for similar things.

Or maybe you ask your current customers some 'Mom Test' type questions.