Extract is a good way to start. I would steep some grain for about 20 minutes at around 160 degrees to add some body.

I don't know what to expect exactly from Einkorn. I would guess that you will get a much lowered efficiency. Meaning you will get less extractable sugars from it. What percentage of Einkorn would you use? My understanding is that it can be hell mashing a very high percentage of wheat in your grain bill. I think the maximum I have done is in the range of 15 to 20%.

I have never made a wheat beer, but I use it in hazy IPAs. I have used it some other beers as well. Off the top of my head I used it in a saison and a belgian tripel. I use chocolate wheat in porter and stout. I'd have to look at my recipes.