I don't know about the cornstarch but for years I had a "Herman" starter, basically a sweet sour dough -- and yes you can use it to make cinnamon rolls. While rolls and such are best the day of baking, the Friendship Bread holds up well for as long as it is around -- which usually isn't long.
The "Amish Friendship Bread" recipe I mostly made with it used pudding mix and I indeed used a variety of flavors. The way I did it, each batch was three of the smaller loaf pans from the dollar store. One stayed home and the other two went to my hubby's work. Both of those recipes are easy to find on searches. Here's basically the one I used for my starter -- although my bread recipe is slightly different.
https://www.cooks.com/recipe/vc9z756...s-version.html
The starter lived in a heavy duty plastic half gallon bucket from a local specialty ice cream maker on top of my large dishes in the cabinet, it fit perfectly height-wise. I've had to give up baking and it was hard to let my Herman go after all the years of care and attention, but I've adjusted to lack of sweet bread.