The course will be made up of videos and we're going to have them professionally filmed all at one time, and we won't be able to do them twice, so I'm not sure how I would make a minimum viable product and get feedback on it. Any suggestions?
Of course you'll save time and money when you produce all videos in a whole batch.
But what about the result? Are you really sure the final product will be accepted by the market? If not, you risk losing big part of the investment.
I think the lean practice should also be applied here in your case.
How about release one or several videos to the public or your old readers for free? Just to see their response to judge if your video will be hot. Also you could gain some initial popularity if the free one is good.
Hope this helps.