Yes, that would all be possible, I’d say. But even with those solutions you would have to do some coding, as all these options don’t import your Ghost blog magically into Kirby, I’m afraid 
The rest API will also only give you some JSON you have to do something with, which will probably not be very different from the big JSON string you already exported, only distributed across multiple endpoints.
The more important stuff that you should do first, at least from my perspective, is think about the data structure/information model you want in your new Kirby site. Then you know what information from your old blog has to go where.