Hello @Ben xyz
Using paper clay slip for casting can help avoid issues like warping and cracking, especially if you need your project to be lightweight for travel. Pre mixed options, such as those from Laguna Clay, make the process easier. With your firing range and large plaster mold, paper clay slip should work well. Since you're planning to paint the sculpture instead of using glaze, paper clay provides a suitable surface. While I don't have direct experience, many artists have found success with this method. It's wise to do some small-scale tests and perhaps consult experienced ceramicists or suppliers for specific advice.