Yes, you can specify the start in pm.sample. pm.find_MAP could be used but we in general discourage strongly on using the MAP as the starting point. The reason being that the gradient around the MAP is usually very small (or even 0), which makes tuning difficult and the possibility of increasing numerical error. I recommend you to try with the out-of-the box default first (i.e., just running pm.sample(1000, tune=1000)).